Journal of Geosciences, 56 (2011), 51–79

DOI: 10.3190/jgeosci.087

Original paper

The Late Miocene Guacimal Pluton in the Cordillera de Tilarán,
Costa Rica: its nature, age and petrogenesis
Vladimír ŽÁČEK1*, Vojtěch JANOUŠEK1, Andrés ULLOA2, Jan KOŠLER3, Sofia HUAPAYA4,Petr MIXA1, Lenka VONDROVICOVÁ1, Guillermo E. ALVARADO5,2Czech Geological Survey, Klárov 3, 118 21 Prague 1, Czech Republic; vladimir.zacek@geology.cz
Escuela Centroamericana de Geología, Universidad de Costa Rica (UCR), San José, Costa Rica
3
Centre for Geobiology and Department of Earth Science, University of Bergen, Allegaten 41, N-5007 Bergen, Norway
4
MINAET, Dirección de Geología y Minas, Apdo. 10104, San José, Costa Rica
5Área de Amenazas y Auscultación Sísmica y Volcánica, PySA, ICE, Apdo. 10032-1000, San José, Costa Rica*
Corresponding author
1
2

The Guacimal Pluton is situated in the Cordillera de Tilarán in the northwestern Costa Rica. It forms an oval-shaped
body strongly elongated in the NW–SE direction. Its dimensions are ~15 × 4–6 km with an exposed surface of 60–70
km2. The pluton intruded basic volcanic rocks of the Aguacate Group (Miocene–Pliocene) and is surrounded by a wide
thermal aureole of calc-silicate metasomatic rocks.
The pluton is mainly formed of monzogranites to granodiorites, which strongly prevail over more basic types occuring scarce and relatively thin dykes and enclaves. The dominant magmatic minerals of this felsic suite are quartz, plagioclase, and K-feldspar with subordinate Mg-rich biotite, amphibole I, and magnetite. Orthopyroxene, Mn-rich ilmenite, Al-poor titanite, rutile, apatite, zircon, thorite, and chalcopyrite are accessories. Secondary minerals, which occur
as fillings of miarolitic cavities and interstices, are quartz II, K-feldspar II, epidote, chlorite, actinolite, ilmenite II and
Al-rich titanite II. The much less frequent mafic suite (mainly quartz diorite to quartz monzodiorite/monzogabbro) is
composed of plagioclase, pargasite, actinolite, K-feldspar, quartz and magnetite, with accessory amounts of opaque minerals, epidote, chlorite, and titanite.
The pluton was emplaced at a depth of c. 3 km, crystallized at temperature of c. 760–800 °C under a relatively highoxygen fugacity (1.6–2.1 log units above the NNO buffer). Increased activities of volatiles (H2O, F) upon cooling areindicated by the presence of highly aluminous, F-rich titanite and other hydrous silicates in miarolitic cavities. The prevailing, felsic rocks of the Guacimal Pluton are high-K calc-alkaline, whereas the mafic suite is nearly exclusively medium-K calc-alkaline in nature. Laser ablation ICP-MS dating of zircons from two granite samples yielded statistically
identical U–Pb ages of 6.3 ± 0.5 and 6.0 ± 0.4 Ma, respectively. The Sr–Nd isotopic compositions are rather primitive(87Sr/86Sr6 = 0.70380–0.70413, ε6Nd ~ +7.3 to +7.9). Narrow range of these values rules out open-system processes suchas magma mixing or assimilation of isotopically contrasting upper continental crust. Instead, the felsic suite is interpreted as either having crystallized from a highly fractionated melt extracted from a plagioclase–amphibole-dominatedcrystal mush in a putative deep crustal reservoir or a product of partial melting of older arc-related rocks, such as intermediate lavas or volcaniclastics or immature psammitic sediments rich in volcanic material. The observed variation in
the felsic suite was most likely produced by low degrees of closed-system fractional crystallization of an assemblage
dominated by feldspars. At least some of the rocks of the volumetrically subordinate mafic suite may represent lithologies rich in the complementary cumulates.
Keywords: granitic rocks, geochemistry, zircon U–Pb age, Guacimal Pluton, Costa Rica, Central American Volcanic Arc
Received: 2 November 2010; accepted: 28 March 2011; handling editor: D. Dolejš
The online version of this article (doi: 10.3190/jgeosci.087) contains supplementary electronic material.

1. Introduction
Plutonic rocks occurring in Central America range from
Precambrian to Pliocene in age. The older intrusions
are mostly situated in the Chortis Block of Guatemala,Honduras and northern Nicaragua but the majority of theyoungest plutonic rocks are concentrated in the Chorotega Block in the SE Costa Rica and Panama, where they
are associated with the Neogene volcanic front (Weyl1980; Donelly et al. 1990; Patino 2007). The igneous
activity of this, now extinct, Late Miocene to Pliocene
volcanic front produced rocks of highly variable nature,
ranging from mostly tholeiitic to calc-alkaline, that form
extensive volcanic deposits and numerous intrusive bodies of various sizes (Denyer and Alvarado 2007, Fig. 1).
The largest plutonic complex is represented by theTalamanca Intrusive Suite, which extends from E Costa
Rica to Panama. This suite includes numerous plutons
www.jgeosci.org

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

85°00’

84°00’NICARAGUA

11°00’

Ca
rib
be
an
Se
a

1

30 km
5

6

10°00’

4

ific O

09°00’
1
2
3
4
5
6
7

cean

7

Guacimal Granite Pluton
Talamanca Intrusive Suite
Puerto Nuevo gabbro
Escazú monzonite–gabbro
Guayacan teschenite
Desmonte monzogabbro
Dominical gabbroand stocks of various sizes where monzogranites dominate but gabbros, diorites, granodiorites, and alkaline
granites are also found (Kussmaul 1987; Abratis 1998;
Drummond et al. 1995; Patino 2007). The age of this igneous complex ranges from 21.6 to 3.5 Ma, with most ofages falling between 12 to 8 Ma; the granites are considered mostly, but not always, to be the youngest whereas
the gabbros are the oldest (Alvarado et al. 1992; de Boeret al. 1995; MacMillan et al. 2004; Patino 2007). The 36
to 3 Ma old intrusive rocks of Panama show a similar
compositional range; granodiorites of this suite are associated with an extensive porphyry copper mineralization(Kessler et al. 1977).
Other Neogene plutonic bodies in Costa Rica are muchless voluminous but very varied. North of the Cordillera de Talamanca, small intrusions of teschenites werereported together with monzonites and syenites withfeldspathoids (Guayacán suite) dated at 4.5 Ma (Azambre
and Tournon 1977; Patino 2007). Other small intrusive
bodies are monzonites to gabbros at Escazú, which weredated from 6.3 to 2.2 Ma (Kussmaul 1987; de Boer et al.
1995), gabbros at Puerto Nuevo (or Dominical Gabbros,c. 14–11 Ma; Appel 1990; de Boer et al. 1995; MacMillan et al. 2004; Gazel et al. 2009) and a small stock of
52

2
3

PANAMÁ

Pac

Fig. 1 Sketch map of Costa Rica withmarked Neogene plutons. Modified
from Denyer and Alvarado (2007).

monzogabbro at Desmonte (2.1 Ma, Bellon and Tournon
1978) (see Fig. 1).
In the NW Costa Rica, the Guacimal Pluton is an isolated body situated in the Cordillera de Tilarán (Chaves
and Sáenz 1974; Cigolini and Chaves 1986; Kussmaul
1987; Denyer and Alvarado 2007). Whereas the large
granitic bodies in the Cordillera de Talamanca were studied extensively because of their ore potential (porphyry
copper deposits), the information about the Guacimal
Pluton remains fragmentary.
Our recent detailed geological survey provided new dataon the size and shape, petrology, geochemistry, and ageof this plutonic body. Preliminary results were presented
in the form of conference abstracts or short reports (e.g.
Žáček et al. 2008) and three published sheets of geological maps on the scale 1 : 50 000 (Žáček et al. 2010a–c).
However most of the information remained in the form ofan unpublished final report (Kycl et al. 2010), which was
handed over to the Costa Rican partner (MINAET, Dirección de Geología y Minas, San José) in March 2010. The
current paper represents the first contribution in a series,
and it is devoted to petrology, mineral chemistry, wholerock and Sr–Nd isotope geochemistry as well as possible
petrogenesis of this intriguing plutonic body.

Miocene Guacimal Pluton, Costa Rica

2. Geological setting

3. Methods

The studied area is situated in the NW Costa Rica, andit belongs to Montes del Aguacate and Cordillera de
Tilarán. It is built by various geological units of Lower
Cretaceous to Quaternary age but mainly of the Miocene
to Pleistocene basaltic and andesitic lavas (Dengo 1962).
The oldest unit is the Complex of Nicoya formed of basalts and peridotites, which represent relics of the Early
Cretaceous ocean floor (Alvarado et al. 1997; Baumgartner and Denyer 2006; Denyer et al. 2006). Several sedimentary and volcanosedimentary formations of Upper
Cretaceous to Miocene age rest unconformably on thisophiolitic suite (Astorga 1987; Denyer and Arias 1991).
However, the basement of the studied area is dominatedby volcanic rocks, mainly lavas and volcaniclastics ofbasaltic to andesitic composition. On the basis of morethan 200 K–Ar ages, the development of this extinct
volcanic arc (Central America Cordillera) started in Early
Miocene (c. 24 Ma). The volcanic activity was episodic
with distinct pulses at 16–17, 4–6, and 1–2 Ma (Bellon
and Tournon 1978; Amos and Rogers 1983; Alvarado etal. 1992; Gillot et al. 1994; Kussmaul et al. 1994; Gans
et al. 2002, 2003).
The older Aguacate Group (c. 23–2 Ma) is cut by
various intrusive and subvolcanic bodies of variable
composition (rhyolites, dacites, andesites to basalts),
and by deeper seated batholiths with smaller stocks ofgranites, granodiorites, diorites and gabbros (including
the Guacimal Pluton). This unit was affected by extensivehydrothermal alteration often associated with the gold
mineralization (Laguna 1983, 1984). The presence ofnumerous gold deposits in this region is obvious from thelocal name Cinturón de Oro or the Golden Belt (Amosand Rogers 1983; Schulz et al. 1987).
After the volcanic activity of the Aguacate Groupceased, several ignimbrite eruptions occurred in Late
Pliocene to Early Pleistocene, relics of which are foundmostly in the eastern part of the studied area (Peñas
Blancas and Alto Palomo units – Villegas 1997, 2004).
After a gap in the Early Pleistocene, the volcanic activity
resumed as a consequence of formation of a new volcanicarc, producing andesitic lavas, various types of pyroclastic rocks and lahars, associated with several rhyodacitic
to andesitic domes.
In contrast to the older Aguacate Group, the Early
Pleistocene Monteverde Formation (1–2 Ma) is characterized by more acidic calc-alkaline volcanism withdominant andesites and by absence of gold-bearing hydrothermal alteration.
The Quaternary period is represented by fluvial sediments, including two levels of terraces and extensive alluvial fans. Accumulations of deposits of giant landslides
occur in the mountains.

The study area belongs to Guanacaste, Puntarenas, andAlajuela provinces, and it included three topographic
map sheets at a scale of 1 : 50 000 (Miramar, Chapernal
and Juntas), thus covering a total area of about 1500 km2.
Magnetic susceptibility of igneous rocks was measured in the field with the KT-5 portable kappameter.
Nine whole-rock samples for chemical analyses and/or
dating (5 granites, 1 quartz diorite and 2 contact hornfelses; see Tab. 1 and Fig. 2 for sample location and further details) were obtained during field geological mapping in March and April 2009 in the Juntas topographic
sheet. Rock samples were crushed in a steel jaw crusher,
homogenized and grinded in an agate ball mill. The fine
powders were analyzed for whole-rock geochemicalcomposition in the Acme Analytical Laboratories Ltd.,
Vancouver, Canada. The major and minor elements were
determined by ICP-OES (4A analytical package) andmost trace elements (Ba, Cs, Ga, Hf, Nb, Rb, Sr, Ta, Th,
U, V, Zr, Y, and REE) by ICP-MS (4B). The dissolutionof the rock powders in both cases followed fusion with alithium metaborate/tetraborate flux and dilute nitric aciddigestion. The analyses of remaining trace elements, andtransition metals in particular (Cu, Pb, Zn, Cr and Ni),
were carried out by ICP-MS following dissolution in aquaregia at 95 ºC (1DX). The detection limits are given in
the Table with the analytical data; further details can befound at http://acmelab.com.
At least 5 kg of three fresh granites (Ju311, Ju328
and Ju346) were crushed in a jaw crusher and zircons
were extracted using Wilfley shaking table, heavy liquid(methylene iodide) and magnetic separation at the Czech
Geological Survey (CGS) at Prague-Barrandov. The zircon concentrates were finally handpicked.
Electron microprobe analyses were carried out
by Cameca SX-100 electron microprobe in the Joint
Laboratory of the Masaryk University and of the CGS,
Brno (R. Škoda, analyst) in the WDS mode. The minerals were analysed at 15 kV accelerating voltage and
10 nA (feldspars, amphiboles, pyroxenes, micas) or 20
nA beam current (titanite, spinels, ilmenite, rutile). The
beam diameter ranged from ~1 µm (rutile, ilmenite,magnetite), 4 µm (majority of silicates) to 6 µm (feldspars). The following standards were used: U – metallic
U, Pb – PbSe, Th – ThO2, P – fluorapatite, Y – YAG, La– LaB6, Ce – CeAl2, Pr – PrF3, Nd – NdF3, Sm – SmF3,
Gd – GdF3, Dy – DyPO4, Er – YErAG, Yb – YbAG,
Al – almandine, Si, Ca, Fe – andradite, Mn – rhodonite,W – scheelite, S – barite, F – topaz, As – InAs, Nb –columbite, Ta – CrTa2O6, Ti – titanite, Zr – zircon, andSc – ScVO4, Mg – pyrope and Sr – SrSO4. Raw data
were reduced by the PAP correction (Pouchou and Pichoir 1985). The detection limits were as follows – Si,
53

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

Tab 1 List of samples analysed

No

Rock

Ju57

amphibole
granite(granophyre)GPScoordinates

Locality

Major minerals Minor minerals(>10 %)(1–10 %)

Accessoryminerals

Minerals of
miaroles /secondarymineralsMS

Analyticalmethodapplied10°12'59.7"N
Guacimal
84°51'00.8"Wquartz,plagioclase,
K-feldspar

amphibole 5 %,magnetite 2 %biotite, titanite,apatite, zircon

epidote,actinolite,
chlorite

2–8

CHA

leucogranite
10°16'01.9"N
Ju98 with amphibole
San Luis
84°49'32.7"Wand biotite

quartz,plagioclase,
K-feldspar

amphibole 3 %,biotite 1 %,magnetite 1 %titanite, apatite,
zirconepidote,actinolite,
chlorite

5–20

CHA

13–15

CHA,
EMPA,
DAT,
Sr–Nd

7–16

CHA,
EMPA,
DAT,
Sr–Nd

Ju311

amphibole
granite withbiotite10°14'06.8"N84°41'42.0"W

San
Antonioquartz,plagioclase,
K-feldspar

amphibole 5 %,biotite 2 %,magnetite 1 %titanite I, ilmenite,
zircon, apatite,orthopyroxene,
pargasite

epidote,chlorite,
actinolite,
titanite IIJu328

amphibole
granite10°16'15.3"NSan Luis
84°49'18.4"Wquartz,plagioclase,
K-feldspar

amphibole 5 %,magnetite 2 %biotite, titanite,
zircon, rutile,
chalcopyrite

chlorite,
epitoteSan
MartínNorte

quartz,plagioclase,
K-feldspar

biotite 3 %,titanite, ilmenite,amphibole 1 %, apatite, zircon,
magnetite 1 %thoritequartz,K-feldspar,
epidote,chlorite,
actinolite

21–27

CHA,
EMPA,
DAT,
Sr–Nd

amphibole I,
K-feldspar,titanite, ilmenite,
epidote, quartz,
apatitemagnetitec. 70 %
secondaryassemblage

60

CHA,
EMPA

epidote,andradite,quartz, calcite,chloritecompletely
secondaryassemblage

0.20

XRD,
CHA,
EMPA

completely
secondaryassemblage

0.1–0.5 XRD, CHA

completely
secondaryassemblage

0.3–0.5

leucogranite
10°14'13.4"NJu346 with biotite and84°45'00.8"W
amphibole

Ju348

amphibolequartz diorite

10°15'53.0"N
84°50'02.0"W

Guariaplagioclase,
amphibole II(actinolite)

Ju321ahornfels(cornubianita)

10°17'22.6"NSan Luis
84°49'40.9"Wdiopside,plagioclase,
K-feldspar,
wollastonite

hornfels
Ju323(cornubianita)

10°17'27.5"NSan Luis
84°49'30.8"Wquartz, calcite,
epidote,chlorite, pyrite,
plagioclase,
smectitediopside

hornfels
Ju327(cornubianita)

10°16'18.9"NSan Luis
84°47'53.7"Wclinozoisite–
epidote,actinolite,
prehnitequartz,plagioclasetitanite, zircon

titanite

CHA,
EMPA

MS – magnetic susceptibility (10-3 SI)

Al, Ca, Cr: 100–200 ppm; Mg, Na, K, Fe, Mn,V, Y, Cl,
Ti, Nb, As, P, S: 200–500 ppm; F, Ni, Zn, La, Ce, U,
Th, Pb: 500–1000 ppm; Pr, Nd, Sm, Gd, Dy, Er, Yb, Ba,
Ta, W: >1000 ppm. The mineral abbreviations used areafter Kretz (1983).
X-ray powder diffraction data were acquired using the Phillips X’pert MPD System (Cu radiation,
graphite secondary monochromator) at CGS, Prague by
I. Haladová. The data were processed by the Bede ZDS
54

Search/Match software (Ondruš and Skála 2004). Thismethod was mainly used for mineral identification inhydrothermally altered rocks including contact metasomatic rocks.
For the radiogenic isotope determinations, samples
were dissolved using a combined HF–HCl–HNO3 digestion. Strontium and neodymium were isolated from thebulk matrix by the exchange chromatography techniques
using Triskem’s Sr resin (equivalent to Sr.spec) and Ei-

Miocene Guacimal Pluton, Costa Ricaa

84°48´

84°50´MonteverdebN

landslides

1 km

10°18´Monteverde Fm.
intensive
silicification
metasomatic rim

San LuisJu323

Guacimal Pluton

Ju321aAguacate Group
GuariaVeracruz

San Martín Norte

San Antonio

Ju328

10°16´

Ju348

Ju327

Guacimal

zo

ne

Ju98

El

Bajo Caliente

En

ca

nt

o

Santa Rosa

El Encanto dam

QUATERNARY
fluvial sediments
sediments ofaluvial fanssediments oflandslides
fluvial terrace
sediments

Ju346
Ju311

10°14´

PLEISTOCENE
Monteverde Formation
andesite,basaltic andesite
grey tuff
porphyritic andesite

MIOCENE – PLIOCENE
acid ignimbrite

Ju57

graniteTM39rhyolite
dacitegabbro10°12´

Aguacate Groupbasalt,basaltic andesite
agglomerate
Bagaces Formationacid tuff
silicification
gold-bearing
alteration
metasomatic rim
lateritization
sample studied(granitoid, hornfels)

Fig. 2 Geological map of the studied area with the sample locations. a – The section from the eastern part of the geological map 1 : 50 000, sheet
3246-IV Juntas (Žáček et al. 2010c). b – Geological sketch map of the Guacimal Pluton, complemented by unpublished manuscript geologicalmap (of Vladimír Žáček) in the neighbouring sheet San Lorenzo.

chrom’s TRU.spec and Ln.spec (Pin et al. 1994; Pin and
Zalduegui 1997; Míková and Denková 2007). Isotopic
analyses of Sr and Nd were performed on a Finnigan
MAT 262 thermal ionization mass spectrometer housed
at CGS in dynamic mode using a single Ta filament for Sr
and double Re filament assembly for Nd. The 143Nd/144Nd

ratios were corrected for mass fractionation to 146Nd/144Nd= 0.7219 (Wasserburg et al. 1981), 87Sr/86Sr ratios assuming 86Sr/88Sr = 0.1194. External reproducibility is
estimated from repeat analyses of the JNdi-1 (143Nd/144Nd= 0.512100 ± 26 2σ, n = 7) and NBS 987 (87Sr/86Sr =0.710244 ± 24 (2σ), n = 14) reference materials.
55

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

Zircon grains for the laser ablation ICP-MS datingwere mounted in 1 inch epoxy-filled blocks and polishedto obtain even surfaces suitable for cathodoluminescence(CL) imaging and laser ablation inductively coupledplasma mass spectrometry (LA ICP-MS) analysis. Prior
to analysis by LA ICP-MS, the sample surfaces werecleaned in 5 % HNO 3, deionized water and ethanol.
Isotopic analyses followed the technique described indetail by Košler et al. (2002). A Thermo-Finnigan Element 2 sector field ICP-MS coupled to a 213 NdYAG
laser (New Wave UP-213) at the Bergen University wasused to measure Pb/U and Pb isotopic ratios in zircons.
The sample introduction system was modified to enable
simultaneous nebulisation of a tracer solution and laser
ablation of the solid sample (Horn et al. 2000). NaturalTl (205Tl/203Tl = 2.3871– Dunstan et al. 1980), 209Bi andenriched 233U and 237Np (> 99 %) were used in the tracer
solution, which was aspirated to the plasma in an Ar–He
carrier gas mixture through an Apex desolvation nebuliser (Elemental Scientific) and a T-piece tube attachedto the back end of the plasma torch. A helium gas line
carrying the sample from the laser cell to the plasma wasalso attached to the T-piece tube. The laser was set up to
produce energy density of ca 1.5 J/cm2 at a repetition rateof 20 Hz. The sample was placed in a low volume (c. 2
cm3) tear-drop ablation cell, which was mounted on acomputer-driven motorised stage of a microscope. During
ablation, the stage was moved beneath the stationary laser
beam to produce a linear raster (c. 50–100 × 60 µm) inthe sample. Typical acquisitions consisted of a 35 second
measurement of analytes in the gas blank and aspirated
solution, particularly 203Tl – 205Tl – 209Bi –233U – 237Np,
followed by measurement of U and Pb signals from zircon, along with the continuous signal from the aspirated
solution, for another 120 seconds. The data were acquiredin time resolved – peak jumping – pulse counting modewith 1 point measured per peak for masses 202 (flyback),
203 and 205 (Tl), 206 and 207 (Pb), 209 (Bi), 233 (U),
237 (Np), 238 (U), 249 (233U oxide), 253 (237Np oxide)and 254 (238U oxide). Raw data were corrected for deadtime of the electron multiplier and processed off line in a
spreadsheet-based program (Lamdate; Košler et al. 2002)
and plotted on concordia diagrams using Isoplot (Ludwig1999). Data reduction included correction for gas blank,
laser-induced elemental fractionation of Pb and U and
instrument mass bias. Minor formation of oxides of U
and Np was corrected for by adding signal intensities
at masses 249, 253 and 254 to the intensities at masses
233, 237 and 238, respectively. Details of data reduction
and corrections are described in Košler et al. (2002) andKošler and Sylvester (2003). Zircon reference material
GJ-1 (609 Ma – Jackson et al. 2004) was periodicallyanalysed during this study and it yielded a concordia ageof 598 ± 12 Ma.
56

4. Geology of the Guacimal Pluton
The Guacimal Pluton is situated in the mountainous areaof S and SW slopes of the Cordillera de Tilarán in the
NW Costa Rica (Guanacaste and Alajuela departments).
The pluton is approximately limited by grid co-ordinates
N 10°11′–10°17′ and W 84°43′–84°50′W. Majority(c. 85 %) of the pluton surface is exposed on the Juntas
map sheet (Žáček et al. 2010c, see Fig 2a), only its easternmost part belongs to the neighbouring San Lorenzo
sheet. The Guacimal Pluton was first described by Chaves
and Sáenz (1974), several chemical analyses were published by Alcorn (1981) and Cigoliny and Chaves (1986),
and its petrography with geochemistry were summarized
by Kussmaul (1987). The pluton, originally called “Formación granito–gabro de Guacimal”, consists of three
predominant rock types: granite (leucogranite, porphyritic granite and granophyric granite), monzodiorite,
and gabbro. The emplacement of the Guacimal Pluton
was followed by extensive hydrothermal alteration andassociated mineralization of the Costa Rican Gold Belt
(Cigolini and Chaves 1986).
The Guacimal Pluton forms an oval-shaped body,strongly elongated in the NW–SE direction; its lengthis ~15 km and the width varies between 4 and 6 km.
The NE contact is situated near San Luis, whereas its
SE contact is located E of San Martín Norte and Bajo
Caliente on the San Lorenzo map sheet (Fig. 2b). The
exposed surface of the pluton does not exceed 60–70 km2,
although previous workers described a much larger extent
of up to 200 km2 (e.g., Kussmaul 1987). Nevertheless, theGuacimal Pluton still represents the largest plutonic bodyin the NW Costa Rica. Fresh rocks are mainly found in
the river valleys (Guacimal and Aranjuez) as well as innumerous streams. However, most of the pluton surface
is deeply weathered, forming sandy to loamy eluvia ofconspicuously light colour (see Fig. 3a–d).
The pluton intruded into the mafic volcanic rocksof the Aguacate Group and is surrounded by a large
metasomatic aureole, which is nearly continuous. The
metasomatic rocks, derived from basalts, basaltic andesites and volcaniclastics of the Aguacate Group havetheir primary textures only rarely preserved. However,frequently they are completely recrystallized showing
both secondary structures and mineral assemblages. Characteristic rocks of the metasomatic aureole are greenish
to black, very fine-grained to massive hornfelses (cornubianitas in Spanish) with conchoidal fracture. They consist of epidote, clinopyroxene, K-feldspar, plagioclase,wollastonite, grossular–andradite, quartz, calcite andpyrite. Hence, they represent a typical Ca-rich contact
metasomatic assemblage. Similar to other occurrences
associated with the granitic intrusions of the Cordillera
de Talamanca (Drummond et al 1995; Kussmaul 2006;

Miocene Guacimal Pluton, Costa Rica

a

b

c

d

Fig. 3 Field appearance and mode of weathering of the Guacimal Pluton. a – Morphology of the Guacimal Pluton outcrops in its central part,
between Cerro San Antonio and Cerro Ojo de Agua. Deep whitish granite eluvia are uncovered by numerous shallow landslides promoted by deforestation and subsequent extensive pasture. b – Residual granite blocks on the mountain crest 1 km E of the Cerro San Antonio (sampling locality Ju311). c – Granite exposure in a creek near San Martín Norte (sampling point Ju346). d – The contact of deeply weathered granite with overlaying younger andesite lava of the Pleistocene Monteverde Formation. Occasional road south of the Cerro San Antonio. The photographs in thisplate and also in Figs 4–5 and 8–10 were taken by Vladimír Žáček.

Ulloa and Delgado 2010), metasomatic rims rich in epidote can be observed.
The southern or south–eastern contact of the pluton
has a tectonic character and follows an important NW–SE
trending fault zone (up to 1 km wide “El Encanto” fault
system) associated with intense hydrothermal alteration,
mainly silicification, which is younger than the contact
metasomatic aureole. A small portion of the pluton andmuch of its metasomatic aureole close to its N and NE
limits are covered by Early Pleistocene Monteverde lava
platform (Fig. 3d) and by large Late Quaternary debris
flows and landslides.

5. Petrology and mineral chemistry

5.1. Granitic rocks
The dominant rocks of the Guacimal Pluton are light,
whitish or pinkish monzogranites to granodiorites withvariable, but generally low amounts of amphibole, brownbiotite and secondary epidote (Fig. 4a–d). Majority ofthese granites are leucogranites as the amount of mafic
minerals is mostly varying between 2 and 5 vol. %. The
individual samples are characterized by similar modaland mineral composition but can show slightly different textures. The granites are mostly medium-grained,
weakly porphyritic to equigranular, without any preferredmineral orientation. The size of phenocrysts rarely exceeds 5 mm; granophyric (micrographic) intergrowths are
frequent. Most of the samples contain abundant miarolitic
cavities, 0.5–4 mm across, filled by a variety of secondary minerals (Figs 5a–f, 6).
The dominant primary minerals are quartz, plagioclase, and K-feldspar with subordinate biotite, amphibole (magnesiohornblende to edenite), and magnetite.
Pargasite, orthopyroxene, Mn-ilmenite, titanite I, rutile,
apatite, zircon, thorite, and chalcopyrite (primary inclusions) are the typical accessory phases. Presenceof accessory tourmaline, mentioned by Kussmaul
57

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

a

b

c

d

e

f

Fig. 4 Hand specimens of the granites and quartz diorite. The granites show a similar appearance, white spots correspond to plagioclase phenocrysts, the greyish or pinkish groundmass is formed by fine K-feldspar and quartz. Observed are tiny dark prismatic amphibole and/or biotite crystals
as well as locally green accumulations of secondary minerals with dominant epidote filling miarolitic cavities. Compare related microphotographs (Figs 5 and 8). a – Whitish to pinkish, medium-grained granite with amphibole and Mg-biotite from the central part of the pluton. The material was obtained from a residual block near Cerro San Antonio (see Fig 3b). b – Whitish to pinkish medium-grained leucogranite with scarce amphibole and biotite from the exposure at San Martín Norte (see Fig. 3c). c – Whitish to greyish, slightly porphyritic amphibole granite with scarce phenocrysts of plagioclase up to 2 mm long. The sample comes from rock exposure at the bridge near the village of San Luis (sampling point
Ju328). d – Greyish micrographic granite (granophyre) sampled in the village of Guacimal from a big isolated block (c. 4 m) transported most probably by river (sampling point Ju57). e – Quartz diorite with conspicuous phenocrysts of amphibole from the dyke 3–5 m thick penetrating hornfels at the road from Guaria to San Luis (sampling point Ju348). f – The same rock with well preserved prismatic amphibole from the boulder
sampled in the Alto Aranjuecito River. The diameter of the coin is 3 cm, the bar corresponds to 1 cm.

58

Miocene Guacimal Pluton, Costa Rica

a

Ju311

b

Ju346

c

Ju328

d

Ju328

e

Ju57

f

Ju57

Fig. 5 Photomicrographs of the studied granites (crossed polarizers if not specified otherwise). a – Medium-grained granite with biotite and amphibole (Ju311). The phenocrysts of plagioclase show fine oscillatory zoning and reach the size of 2–6 mm, but the matrix is also relatively coarse grained (0.1–1 mm). Micrographic intergrowths are locally observed. The rock contains brown biotite and pale-brown amphibole up to 3 mm
long. Occasional small miarolitic cavities are filled with secondary chlorite and epidote. b – Medium-grained porphyritic granite with biotite, locally showing micrographic structure. The plagioclase phenocrysts (or their clusters) are up to 5 mm across, matrix is also relatively coarse grained (0.5–1 mm). Abundant are tiny miarolitic cavities filled by euhedral secondary minerals. c – Porphyritic granite with amphibole (Ju328), thesize of the phenocrysts reaches 0.5–2 mm. Relatively abundant brown amphibole forms long-prismatic phenocrysts up to 3 mm long. Prevailingmatrix (c. 60 %) is fine-grained (0.05–0.2 mm). Plane polarized light. d – The same sample, crossed polarizers. e – Porphyritic medium-grained
granite (granophyre) with phenocrysts of plagioclase up to 5 mm long (Ju57). Very fine micrographic (granophyric) intergrowths of quartz andK-feldspar are seen. The rock contains prismatic brown amphibole up to 2 mm long. Biotite, if originally present, was completely chloritized.
Abundant miarolitic cavities are filled by euhedral epidote, actinolite and chlorite. Plane polarized light. f – The same sample, crossed polarizers.
The white bar in each photomicrograph is 1 mm long.

59

Ep

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

a
Kfs

b

Ep

Ilm IIChl

Ab
Ep

Ttn II
Ttn

Act

Pl-r

Ilm
Qtz

Kf sII
Chl

Qtz

Pl-c

Ep

Fig. 6 Back-scattered electron (BSE) images of miarolitic cavities in the Guacimal granites. a – Miarolitic cavity in the sample Ju363 filled by Kfeldspar II (adularia, Kfs II), chlorite (Chl), epidote (Ep) and hornblende II (Act). Other groundmass minerals are K-feldspar (Kfs I), albite (Ab),quartz (Qtz), ilmenite (Ilm) and titanite (Ttn). b – Miarolitic cavity in the sample Ju328 filled by clearly secondary ilmenite II, titanite II, chlorite and epidote (for symbols see Fig. 9a). Note calcic cores (Pl-c) and sodic rims (Pl-r) of the large crystals of plagioclase. Photomicrographs by
Radek Škoda.

(1987), was not confirmed. Among mafic minerals,
amphibole mostly prevails over biotite. In the sample
Ju311, two generations of plagioclase were observed:(1) a single oval xenocryst 5 mm across with numerous anhedral inclusions of edenite (up to 150 µm long)and scarce orthopyroxene (up to 20 µm long, always
rimmed by edenite) in the centre of the xenocryst, and(2) predominant prismatic plagioclase. The xenocryst
was probably not in equilibrium with other minerals in
the groundmass and it probably represents a relic of acrystal captured from a more basic magma.
The amphibole in the groundmass is brown to pale
brown, slightly pleochroic. It forms euhedral to subhedral, mostly prismatic crystals up to 3 mm long. Itsamount can reach up to ~5 vol. %. Locally, it is partiallyreplaced by pale brown secondary actinolite or chlorite.
Biotite is brown, strongly pleochroic, subhedral, reaching 2 mm across but mostly smaller. It accounts for
up to ~ 4 vol. % but in some samples it is completely
lacking. Biotite is more or less (sometimes completely)chloritized. Magnetite is ubiquitous, occurring as euhedral to anhedral equant grains up to 0.5 mm in diameter,
amounting to 0.5–2 vol. %. Titanite I forms subhedralgrains up to 200 µm long in the interstitial space among
the primary minerals. Secondary minerals, which either replace mafic primary phases or occur as euhedral
crystals in miarolitic cavities and interstitial space inthe groundmass, are quartz II, K-feldspar II (adularia),
epidote, chlorite, amphibole II (actinolite), ilmenite II
and titanite II. Epidote is the most abundant secondary mineral, forming yellow–green euhedral (prismaticto acicular) crystals up to 2 mm long in the miarolitic
cavities. Alternatively it can be microscopic, occurring
as clusters of subhedral crystals replacing plagioclase in60

the matrix. Ilmenite II occurs as rosette-like aggregatesup to 100 µm long grown in miarolitic cavities as theoldest phase. Titanite II occurs either as euhedral crystals
in miarolitic cavities or as rims of ilmenite II.
Chemical composition of rock-forming minerals wasanalyzed by electron microprobe in samples Ju311, Ju328
and Ju346 (Tab 2, Appendix 1–6) and it is illustrated inFig. 7.
Plagioclase is labradorite to andesine (rarely albite)with calcic centres and more sodic rims (An58–04), poor in
SrO (< 0.20 wt. %) and BaO (< 0.19 wt. %) but with increased K2O contents (0.13–0.97 wt. %). Rare xenocrystof plagioclase in the sample Ju311 shows discontinuous
zoning with small core strongly enriched in Ca (An86)
and a wide oscillatory-zoned rim (An48–13), with a gap
between An30 and An21. In addition, inclusions of edenite
and orthopyroxene occur in the calcic centre.
K-feldspar contains sharply bound domains rich in
BaO (4.2–5.6 wt. %); outside of these domains the concentration of BaO ranges between 0.16 and 1.29 wt. %,whereas the Na 2O content is 1.70–3.83 wt. %. The
K-feldspar from miarolitic cavities is both Na- and Bapoor (1.40 wt. % Na2O and 0.72 wt. % BaO).
Mg-rich biotite (X Mg = molar Mg/(Mg + Fe) ratio= 0.66–0.75) is rich in TiO2 (2.92–5.43 wt. %) and F(1.55–2.40 wt. %) with high Cl concentrations (0.31–0.40
wt. %). Primary amphibole I corresponds to magnesiohornblende, less frequently to edenite (Si = 6.96–7.46
apfu, (Na + K) A ~ 0.3–0.6 apfu, X Mg = 0.67–0.78)
whereas fibrous secondary amphibole II is actinolite (Si= 7.72–7.78 apfu, XMg = 0.80). Amphibole occurring as
inclusions together with orthopyroxene in the plagioclase(sample Ju311) is edenite (Si = 6.91 apfu, (Na + K)A =0.66 apfu, XMg = 0.70).

Miocene Guacimal Pluton, Costa Rica

Tab 2 Chemical composition of amphiboles (wt. %, apfu) and Hbl–Pl geothermobarometry
sampleJU 346JU 328JU 328JU 328JU 311JU 311JU 311JU 348JU 348JU 348rock
granitegranitegranitegranitegranitegranitegranitedioritedioritedioritecomment
secondaryprimary
primary
secondaryprimary
primary
primary
primary* secondary secondary
52.18
47.92
48.09
54.80
46.51
46.89
46.95
41.12
48.60
53.55
SiO2
TiO2
0.61
1.63
1.46
0.08
1.60
1.65
1.62
2.30
1.29
0.35
Al2O3
3.57
6.13
5.83
1.72
6.36
6.44
6.19
12.22
5.90
2.66
Fe2O3calc
1.84
2.57
2.95
1.91
0.70
1.02
2.10
6.87
2.86
2.10
FeOcalc
7.38
9.83
9.71
6.36
11.78
11.21
10.34
5.51
7.52
6.44
MgO
17.90
15.25
14.83
18.58
15.32
15.77
15.60
14.33
17.23
19.14
MnO
0.75
0.43
0.50
0.64
0.54
0.43
0.45
0.18
0.40
0.33
CaO
11.42
11.50
11.72
12.64
11.16
11.28
11.28
11.55
11.85
12.28
Na2O
1.76
1.61
1.44
0.60
2.14
1.96
1.40
2.51
1.17
0.48
K 2O
0.50
0.54
0.47
0.12
0.59
0.55
0.57
0.46
0.63
0.23
F
2.10
0.81
0.82
0.72
1.82
1.40
0.82
0.90
0.63
0.49
Cl
0.12
0.13
0.12
0.04
0.14
0.15
0.16
0.00
0.19
0.17
H2Ocalc
1.07
1.62
1.61
1.76
1.12
1.33
1.59
1.58
1.72
1.83
-O=F+Cl
0.91
0.37
0.37
0.31
0.80
0.62
0.38
0.38
0.31
0.24
Total
99.94
96.10
97.62
98.00
98.59
98.64
97.25
97.25
97.97
98.01
Formula after Holland and Blundy (1994) assuming 24 O+OH+F+Cl) and OH+F+Cl = 2
Si
7.435
6.994
7.050
7.749
6.901
6.897
6.934
6.053
7.015
7.571
Aliv
0.565
1.006
0.950
0.251
1.099
1.103
1.066
1.947
0.985
0.429
Sum T
8.000
8.000
8.000
8.000
8.000
8.000
8.000
8.000
8.000
8.000
Alvi
0.035
0.050
0.057
0.036
0.014
0.013
0.012
0.172
0.019
0.015
Ti
0.065
0.179
0.160
0.008
0.178
0.183
0.179
0.254
0.140
0.037
Fe3+
0.197
0.283
0.325
0.203
0.078
0.113
0.233
0.761
0.311
0.224
Mg
3.801
3.317
3.239
3.915
3.388
3.457
3.433
3.143
3.706
4.034
Mn
0.091
0.053
0.062
0.077
0.067
0.053
0.056
0.022
0.049
0.040
Fe2+
0.811
1.119
1.156
0.752
1.275
1.181
1.087
0.647
0.776
0.650
Sum M1, 2, 3
5.000
5.000
5.000
5.000
5.000
5.000
5.000
5.000
5.000
5.000
Fe
0.068
0.081
0.035
0.000
0.187
0.198
0.191
0.030
0.133
0.112
Ca
1.744
1.799
1.841
1.906
1.775
1.777
1.786
1.821
1.833
1.860
Na
0.188
0.120
0.125
0.094
0.038
0.025
0.023
0.148
0.035
0.029
Sum M4
2.000
2.000
2.000
2.000
2.000
2.000
2.000
2.000
2.000
2.000
Na
0.298
0.336
0.285
0.069
0.578
0.534
0.378
0.567
0.294
0.102
K
0.091
0.100
0.087
0.022
0.111
0.103
0.107
0.087
0.116
0.042
Sum A
0.390
0.436
0.372
0.091
0.689
0.636
0.485
0.654
0.410
0.144
OH
1.023
1.590
1.586
1.665
1.108
1.309
1.576
1.576
1.665
1.739
F
0.948
0.378
0.384
0.325
0.857
0.653
0.385
0.425
0.289
0.221
Cl
0.029
0.032
0.030
0.010
0.035
0.038
0.039
0.000
0.046
0.040
Sum OH-site
2.000
2.000
2.000
2.000
2.000
2.000
2.000
2.000
2.000
2.000
Sum cations
15.39015.43615.37215.09115.68915.63615.48515.65415.41015.144
Mg/(Mg + Fe2+)
0.760
0.663
0.648
0.783
0.678
0.691
0.687
0.629
0.741
0.807
Fe3+/(Fe2++ Fe3+)
0.183
0.191
0.214
0.213
0.051
0.076
0.154
0.529
0.255
0.227
Altot
0.599
1.055
1.007
0.287
1.112
1.117
1.078
2.120
1.004
0.444
XAb
0.602
0.564
0.442
0.403
0.452
XAn
0.351
0.398
0.536
0.580
0.528
T and P results based on Anderson´s spreadsheet for Hbl–Pl thermobarometry (Anderson 1996) using Holland and Blundy (1994) Hbl–Pl thermometry calibration for the reaction: edenite + albite = richterite + anorthite. T Otten – temperatures based on Ti in amphibole following
Otten (1984)
T (AS) (°C)
763
769
784
762
720
P (AS) (kbar)
0.9
0.7
0.8
1.2
1.7
T Otten (°C)
760
738
760
765
761
851
T, P and fO2 results calculated by spreadsheet of Ridolfi et al. (2010)
T (°C)
802
791
855
857
842
984
uncertainty
22
22
22
22
22
22
P (kbar)
0.87
0.81
0.93
0.93
0.88
4.01
uncertainty
0.10
0.09
0.10
0.10
0.10
0.44
depth (km)
3.3
3.1
3.5
3.5
3.3
15.2
∆NNO
1.6
1.6
1.9
2.0
2.1
1.0
log fO2
–12.2
–12.5
–10.9
–10.7
–10.9
–9.5
uncertainty
0.4
0.4
0.4
0.4
0.4
0.4
* the composition used for geochemical modelling61

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

a

Kf

Wo

b

Ju328 granite
Ju346 granite
Ju311 granite
Ju311 Pl-xenoX

HdDi

Ju348 diorite
Ju321a hornfels
Ju 327 hornfels

augitepigeonite

1.0

tremolite

Mg/(Mg+Fe)

En

An

Ab

magnesiohornblende (Na+K)A < 0.5
edenite (Na+K)A > 0.5

Fstschermakite (Na+K)A < 0.5
pargasite (Na+K)A > 0.5cactinolite

0.5

ferro-actinolite
0.0

8.0

ferrotschermakite

ferrohornblende
6.5

7.0

7.5

6.0

5.5

Si (apfu)

e

d
3.0

1.0

Altot (apfu)

Mg/(Mg+Fe)

eastonitesiderophyllite

2.0

ripidolite

clinochlore

penninitethuringite

chamositedelessite

0.48

phlogopite

annite

0.0

1.0

Fe

0.5

Mg

2.75

3.10

Si (apfu)

Fig. 7 Chemical composition of feldspars, pyroxenes, hornblende, dark mica and chlorite from granitic rocks and hornfelses. a – Ab–Kfs–An plot for
feldspars. b – En–Fs–Wo plot for pyroxenes. c – The diagram for calcic amphiboles characterized by the following site occupancies: Ca B >1.5, CaA<0.5, Ti<0.50 and (Na + K)A<0.5 apfu, only the shaded compositions correspond to amphiboles with (Na + K)A>0.5 apfu (calculated on the basis of 24(O + OH + F), assuming OH + F = 2, following Leake at al. 1997). d – Mg/(Mg + Fe) vs. Altot plot (apfu) of dark mica (calculated on the basis of 12(O + OH + F + Cl), assuming OH + F + Cl = 2). e – Si vs. Mg/(Mg + Fe) plot for chlorites (calculated on the basis of 18 (O+OH), assuming 8 OH).

62

Miocene Guacimal Pluton, Costa Rica

Orthopyroxene is Fe-rich enstatite (XMg = 0.62–0.67)
with increased Al2O3 (0.51–2.02 wt. %) and CaO concentrations (0.92–2.68 wt. %). Magnetite is relatively
poor in minor elements: 0.24–1.18 wt. % TiO2, 0.13–1.65
wt. % Al2O3, 0.27–0.68 wt. % V2O3. A small inclusion ofchalcopyrite was found enclosed in magnetite. Relatively
abundant accessories are apatite and zircon. Thorite up
to 3 µm across is very rare. Ilmenite forms (1) individual
poikilitic aggregates intergrown with apatite, (2) thin
exsolution lamellae in magnetite, or (3) crystallized
in miarolitic cavities as the oldest secondary phase.
All types of ilmenite are rich in MnO (8–21 wt. %),which corresponds to 17–44 mol. % of the pyrophanite
component; the highest Mn concentrations were foundin the exsolution lamellae. Titanite I found in the rockmatrix is poor in Al2O3 and F, unlike titanite II in the
miarolitic cavities and titanite overgrowths on ilmenitewith 5.9–8.2 wt. % Al2O3 and 2–3 wt. % F. Epidote contains 10.5–15.8 wt. % of Fe2O3tot; chlorite corresponds
to clinochlore (Si = 2.88–2.95 apfu, XMg = 0.65–0.68);
see also Fig. 7.

5.2. Quartz diorite

bole II and yellowish epidote. Overgrowths of highly
aluminous titanite replacing epidote were observed(Figs 4e–f, 8).
Brown amphibole I is titanian pargasite (Si = 6.05–
6.15 apfu, Ti = 0.26–0.29 apfu, XMg = 0.68–0.69). Primary
K-feldspar is enriched in Na2O (0.68–1.98 wt. %), BaO(0.82–3.74 wt. %) and SrO (0.08–0.16 wt. %). Plagioclase is mostly oligoclase but rarely as calcic as labradorite (An24–62) poor in BaO (< 0.09 wt. %) but with slightly
increased K 2O (0.48–0.64 wt. %) and SrO contents(0.10–0.17 wt. %). Amphibole II is magnesiohornblendeto actinolite (Si = 7.06–7.67 apfu, XMg = 0.75–0.83). Magnetite contains 0.31–0.88 wt. % TiO2, 0.04 wt. % Al2O3
and 0.49 wt. % V2O3, ilmenite hosts 5.3–8.3 wt. % MnO,
corresponding to 13–18 mol. % pyrophanite. Epidote isrelatively Fe-rich (11.4–12.7 wt. % Fe2O3tot = 0.66–0.73
Fe3+ apfu). Titanite, which is found as overgrowths on
epidote, is extremely rich in Al2O3 (11.26 wt. %) and F(3.93 wt. %).

6. Country rocks of the Guacimal Pluton

The only quartz diorite sample studied is strongly
porphyritic and composed essentially of dominant plagioclase and pale green amphibole II. Minor constituents are brown amphibole I, K-feldspar and quartz; an
opaque mineral, epidote, chlorite and titanite are common accessories. Amphibole I, K-feldspar and magnetite
are primary phases formed by magmatic crystallization,
and were mostly replaced by a mosaic of fine prismatic(probably recrystallized) plagioclase, pale green amphi-

The Guacimal Pluton is surrounded by thermal aureole
several hundred metres to c. 1.5 km wide, which overprints the Aguacate Group country rocks. The exocontact
is transitional, with the intensity of thermal effects decreasing gradually away from the contact with granite.
The contact aureole is most probably continuous but
along the northern contact it is locally hidden below
the younger Monteverde Formation. In its SW part, thepluton is truncated by the El Encanto zone (Fig. 2b), a
fault system striking NW–SE, which follows the granite

a

b

Ju348

Ju348

Fig. 8a – Photomicrographs of the quartz diorite sample Ju348 (see also Fig. 4e). Primary mineral assemblage was formed predominantly by prismatic brown amphibole (up to 7 mm long), plagioclase and some quartz. However, the rock is strongly recrystallized to a fine mosaic of secondary prismatic plagioclase, acicular greenish actinolite with abundant epidote and chlorite, occurring both in the matrix and in veinlets. It is difficult to recognize primary and secondary phases due to cloudy matrix. Plane polarized light. b – The same sample, crossed polarizers. The bar
cor­responds to 1 mm.

63Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

a

b

c

d

Fig. 9 Field photographs of metasomatic hornfelses from the thermal aureole of the Guacimal Pluton. a – Exposure of greyish–green banded hornfelses at the Guacimal River near San Luis (Ju323). b – Banded and undulated sequence of black fine-grained hornfelses in the metasomatic zone
at the road to Bajo Caliente near the El Encanto reservoir dam. c – Sample of medium-grained speckled hornfels composed mainly of clinozoisite–epidote, chlorite, actinolite and calcite from the mountains E of San Luis (Ju327). d – Fine grained hornfels with the veinlet of andradite which
represents typical hornfels “cornubianita”. North-west of San Luis, sample Ju321a. The bar is 1 cm long.

aJu321ab

Ju327

Fig. 10 Photomicrographs of contact metasomatic rocks shown in Figs 9c–d. a – The sample Ju321a with an andradite veinlet. The matrix is composed of fine-grained mosaic with dominant diopside, quartz, wollastonite, K-feldspar and andradite. b – Microstructure of the sample Ju327 formed by prevailing hornblende, clinozoisite–epidote, prehnite and chlorite. Crossed polarizers, bars correspond to 1 mm.

64Miocene Guacimal Pluton, Costa Rica

contact for at least 15 km. This structure is accompanied
by intense hydrothermal alteration, mainly silicification with subordinate amounts of pyrophyllite, alunite,
sericite, kaolinite, and several other, rather rare minerals(Fig. 2a–b).
Contact metasomatic rocks are highly variable withapple green, dark grey–green to nearly black colour(Fig. 9a–b). Two main types can be distinguished:(1) fine- to medium-grained speckled rocks with relicsof primary volcanic structures and magmatic minerals(e.g., former phenocrysts), and (2) very fine-grained
hornfelses with conchoidal fracture, where primaryminerals and structures were completely obliterated bya newly formed assemblage (Fig. 9c–d). The contact
metasomatic rocks can also show bands, several cm–dm
thick, which differ in colour and grain size. Alteredrocks including hornfelses are also characterized bymostly low magnetic susceptibilities (0.1–0.5 × 10 -3
SI), which indicate that the original magnetic mineral
was decomposed.
The coarse-grained contact-metasomatic rocks consist of abundant epidote–clinozoisite and chlorite, withrare accumulations of calcite. The amount of epidote,
which is the most characteristic secondary mineral,
increases from several up to over 50 vol. %. The calcsilicate hornfelses are very fine-grained with characteristic conchoidal fracture. They contain pyrite (disseminated and veinlets), epidote or, rarely, andradite-richgarnet. The following phases were identified by X-ray
diffraction or electron microprobe: Ca-rich garnet,
clinozoisite–epidote, plagioclase, hedenbergite, amphibole, K‑feldspar, wollastonite, chlorite, prehnite, quartz,
calcite, pyrite, titanite, and smectite (see Fig. 10a–b).
Mineral chemistry of hornfelses was studied in two
samples (Appendix 5–6).
In the sample Ju321a, plagioclase is poorly zoned
andesine–labradorite, An 47–53 with elevated concentrations of K 2O (0.35–1.17 wt. %) and FeOt (0.52–0.81
wt. %). K-feldspar contains slightly elevated Na 2O(1.15–1.85 wt. %) and BaO contents (0.37–0.52 wt. %).
Clinopyroxene is hedenbergite (XMg = 0.33–0.41) with
0.74–1.19 wt. % Al 2O 3 and 0.27–0.31 wt. % Na 2O.
Ca-rich garnet corresponds to andradite–grossularsolution (Grs 04–52 Adr44–98 Sps<04), poor in oxides of Ti,
Cr and Mg (all < 0.10 wt. %). Epidote contains 9.65
wt. % Fe2O3tot.
The sample Ju327 is composed mainly of quartz, amphibole, plagioclase, clinozoisite–epidote, and prehnite.
Amphibole corresponds to magnesiohornblende or pargasite (Si = 6.34–7.17 apfu, XMg = 0.59–0.57). Plagioclase
is labradorite to bytownite (An65–82) poor in BaO and withelevated SrO (0.04–0.35 wt. %). Clinozoisite–epidote occurs as several successive generations with the Fe2O3tot
varying widely between 3.08 and 9.42 wt. %. Prehnite
formed as the youngest phase. Accessory titanite is poorin Al2O3 (1.72 wt. %) and F (0.09 wt. %).

Tab 3 U–Pb dating
Analysis 207Pb/235U ± 1 σ 206Pb/238U
Sample JU-311, U–Pb age 6.3 ± 0.5 Ma#1
0.01840.00210.0010#20.01450.00320.0010#3
0.01610.00280.0011#4
0.02570.00790.0012#50.02410.00370.0011#6
0.01930.00270.0011#70.00690.00140.0011#80.00520.00200.0011
Sample JU-328#90.01260.00150.0013#100.01770.00450.0015#110.01040.00230.0015#120.01140.00280.0011#13
0.01280.00270.0015#140.00630.00090.0009Sample JU-346, U–Pb age 6.0 ± 0.4 Ma#15
0.01310.00340.0010#16
0.01260.00170.0009#170.00730.00150.0010#18
0.02570.00410.0011#19
0.03160.00710.0013#20
0.04190.00540.0013#21
0.05860.01020.0015#220.01040.00230.0009#230.03060.00630.0011

ISOTOPIC RATIOS±1σ
Rho 238U/206Pb±1σ0.00010.00010.00010.00020.00010.00010.00020.0001

0.31
0.21
0.28
0.30
0.38
0.31
0.37
0.18

980.4
1016.1
908.1
841.0
931.4
918.3
883.8
930.2

0.00010.00010.00010.00010.00010.0001

0.23
0.14
0.13
0.21
0.23
0.27

0.00010.00010.00010.00010.00020.00010.00020.00010.0001

0.16
0.24
0.17
0.30
0.29
0.34
0.46
0.19
0.22

CALCULATED AGES (Ma)Pb/235U ± 1 σ 206Pb/238U ± 1 σ

Pb/206Pb

±1σ

68.6
93.0
89.6
155.5
110.9
80.7
133.0
124.1

0.13100.10700.10630.15680.16270.12880.04440.03520.01930.01690.01880.03440.02330.02030.00800.0076

18.5
14.6
16.3
25.8
24.2
19.4
7.0
5.3

2.1
3.2
2.8
7.8
3.7
2.7
1.4
2.0

6.6
6.3
7.1
7.7
6.9
7.0
7.3
6.9

0.5
0.6
0.7
1.4
0.8
0.6
1.1
0.9

748.6
683.3
683.2
930.7
687.1
1145.1

41.7
48.4
40.9
98.2
65.1
86.0

0.06840.08780.05140.0772
0.06370.05260.00810.01230.00760.01440.01720.0066

12.7
17.8
10.5
11.5
12.9
6.4

1.5
4.5
2.3
2.9
2.7
0.9

8.6
9.4
9.4
6.9
9.4
5.6

0.5
0.7
0.6
0.7
0.9
0.4

999.5
1066.8
986.0
944.5
790.6
774.5
657.6
1066.1
913.0

84.7
71.1
69.9
92.0
102.2
68.2
105.3
88.4
84.9

0.0951
0.09770.05190.17570.18100.23550.27950.08020.20230.02300.00970.00740.02490.02620.02630.03740.01300.0299

13.2
12.7
7.3
25.7
31.6
41.7
57.8
10.5
30.6

3.4
1.7
1.5
4.1
7.0
5.2
9.8
2.3
6.3

6.4
6.0
6.5
6.8
8.1
8.3
9.8
6.0
7.1

0.5
0.4
0.5
0.7
1.1
0.7
1.6
0.5
0.7

207

207

65

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

L. Anderson. The temperature estimates are based on theamphibole–plagioclase thermometric calibration of thereaction edenite + albite = richterite + anorthite (Holland
and Blundy 1994), and on the Ti solubility in amphibole
The temperature and pressure of magmatic crystal(Otten 1984). Amphibole equilibria were also used to
lization were assessed using amphibole–plagioclase
estimate oxygen fugacity (Ridolfi et al. 2010) (Tab. 2).
thermobarometry (Anderson and Smith 1995; Anderson
The temperatures calculated for five amphibole and1996). The temperature and pressure were estimatedplagioclase pairs from the felsic Guacimal suite fall
iteratively by a spreadsheet that was kindly provided byin the interval 720–857 °C (mostly
ranging between 760 and 800 °C).
0.6
The pressures vary between 0.7 andData-point error ellipses are at 68.3% confidence
1.7 kbar with a distinct maximum at
0.8–0.9 kbar. One sample from the
0.5
mafic suite yielded temperatures between 851 and 984 °C and pressure of
JU-311c. 4 kbar. Oxygen fugacity estimated
6.3
±
0.5
Ma
0.4
for the felsic suite is 1.6–2.1 log units
MSWD = 0.53
above the nickel–nickel oxide buffer(NNO), whereas the estimate for the
0.3
mafic suite is ΔNNO = +1.0.
207

Pb/206Pb

7. Thermobarometry and oxybarometry ofmagmatic crystallization

0.2

8.

0.1

0.0
100

28 20

12

300

500

6

8
700
238

900

1100

1300

1500

U/206Pb

0.6

Data-point error ellipses are at 68.3% confidence
0.5

JU-346
0.4

0.3

207

Pb/

206

Pb

6.0 ± 0.4 Ma
MSWD = 0.56

0.2

0.1

0.0
100

28 20

12

300

500

8
700
238

U/

6
900

206

1100

Pb

Fig. 11 Inverse concordia diagrams for the samples Ju311 and Ju346.

66

1300

1500

LA ICP-MS zircon age

Zircon from granite samples Ju311,
Ju328 and Ju346 forms prismatic andstubby crystals up to 150 μm long. The
CL imaging revealed oscillatory zoning
combined with sector zoning, which
are both indicative of crystallizationfrom the melt for most of the grains(Corfu et al. 2003). However, somezircon grains, especially in the sample
Ju328, also contain discrete domains intheir cores that can be interpreted as anolder, inherited component.
Results of the LA ICP-MS dating
are summarized in Tab. 3 and thedata are shown on inverse concordia
diagrams in Fig. 11. Most of the data
points plot away from the concordia
curve suggesting presence of variable amounts of common Pb in theanalysed zircons. Since the accurate
correction for common Pb via measurement of 204Pb is difficult due toisobaric interference of 204Hg present in the ICP gas, we have used theinverse Tera-Wasserburg projection
to calculate U–Pb ages for the radiogenic Pb component. The data regression lines were anchored to common
Pb composition corresponding to thetwo-stage model of crustal Pb evolu-

Miocene Guacimal Pluton, Costa Rica

Tab. 4 Major- and trace-element whole-rock geochemical data
SampleRock type
SiO2
TiO2
Al2O3
Fe2O3t
MnO
MgO
CaO
Na2O
K 2O
P 2O 5C(tot.)S(tot.)LOI
Total
K2O/Na2O
A/NK
A/CNK
mg#
CaO/Na2O
Cs
Rb
Sr
Ba
Th
U
Zr
Hf
Nb
Ta
Pb
Ga
Sn
Ni
Co
V
Sc
Cu
Zn
As
W
Au (ppb)
K/Rb
Rb/Sr
Rb/Ba
Y
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Eu/Eu*
LaN/YbN
LaN/SmN
ΣREE

Detection
limit
0.01
0.01
0.01
0.04
0.01
0.01
0.01
0.01
0.01
0.01

0.1
0.1
0.5
1
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.5
1
0.1
0.2
8
1
0.1
1
0.5
0.5
0.5

0.1
0.1
0.1
0.02
0.3
0.05
0.02
0.05
0.01
0.05
0.02
0.03
0.01
0.05
0.01

Ju348
qtz diorite
54.51
0.92
16.20
10.04
0.15
4.14
6.45
3.40
1.07
0.17
<0.02
<0.02
2.60
99.69
0.32
2.40
0.88
45.0
1.90
2.2
20.8
540.7
619
1.7
1.1
82.3
2.2
3.6
0.2
3.2
17.0
1
5.4
24.0
313
28
49.9
29
6.1
0.5
3.0
427.0
0.04
0.03
21.6
8.9
22.6
3.32
15.7
3.98
1.09
4.21
0.68
4.09
0.79
2.29
0.34
2.29
0.33
0.81
2.62
1.41
70.6

Ju98
granite
68.83
0.43
14.91
3.02
0.11
0.77
2.44
3.56
3.86
0.11
<0.02
<0.02
1.60
99.68
1.08
1.49
1.03
33.6
0.69
1.5
89.1
352.5
1927
6.2
2.3
198.7
5.4
8.8
0.5
9.7
13.1
1
6.9
5.0
62
8
28.2
36
3.6
0.6
4.8
359.6
0.25
0.05
26.7
27.1
54.2
6.69
24.4
4.67
0.93
4.21
0.71
4.13
0.87
2.76
0.43
3.02
0.47
0.64
6.05
3.65
134.6

Ju328
granite
69.56
0.40
14.53
3.18
0.08
0.85
2.43
3.60
3.44
0.09
0.03
<0.02
1.50
99.71
0.96
1.51
1.03
34.6
0.68
0.9
85.4
348.4
1553
5.1
2.0
193.1
4.4
7.2
0.4
2.8
13.1
<1
6.8
5.8
66
9
39.8
31
1.9
0.5
8.1
334.4
0.25
0.06
21.4
18.2
36.7
4.32
17.6
3.57
0.71
3.36
0.56
3.41
0.69
2.28
0.34
2.39
0.37
0.63
5.13
3.21
94.5

Ju57
granite
69.81
0.33
14.70
2.66
0.10
0.78
2.82
3.73
3.59
0.07
0.04
<0.02
1.10
99.75
0.96
1.47
0.97
36.7
0.76
2
84.1
410.8
1695
5.7
2.6
163.4
4.4
6.8
0.4
5.2
12.9
<1
4.1
4.5
45
7
19.1
33
1.0
0.5
4.0
354.4
0.21
0.05
21.4
25.8
48.4
5.67
21.5
3.75
0.81
3.23
0.53
3.30
0.67
2.14
0.32
2.44
0.38
0.71
7.13
4.33
118.9

Ju311
granite
70.73
0.35
14.48
2.59
0.07
0.79
2.50
3.61
3.68
0.08
<0.02
<0.02
0.80
99.72
1.02
1.46
1.00
37.7
0.69
1.2
88.2
367.7
1930
5.4
2.3
179.1
4.6
6.9
0.4
2.7
12.9
<1
4.6
4.6
52
7
16.8
25
0.6
0.6
1.6
346.4
0.24
0.05
20.2
21.0
41.9
4.79
17.3
3.46
0.75
3.20
0.52
3.27
0.64
2.09
0.32
2.27
0.34
0.69
6.24
3.82
101.9

Ju346
granite
71.55
0.29
14.15
2.26
0.10
0.64
2.21
3.55
4.00
0.07
0.03
<0.02
0.90
99.77
1.13
1.39
1.00
35.9
0.62
1.4
93.7
307.0
1679
6.5
2.9
147.6
4.0
7.0
0.4
10.5
13.1
<1
7.8
3.8
35
6
17.6
33
1.8
0.5
4.4
354.4
0.31
0.06
19.0
24.0
46.0
5.14
19.3
3.35
0.68
3.07
0.50
2.98
0.61
1.90
0.32
2.33
0.35
0.65
6.94
4.51
110.5

Ju327
hornfels
45.38
0.51
14.48
8.78
0.15
9.69
13.92
0.96
0.15
0.05
0.09
<0.02
5.50
99.68
0.16
8.31
0.54
68.6
14.50
0.3
2.4
464.3
79
0.2
0.1
19.9
0.6
0.6
0.1
1.0
13.7
<1
42.0
42.5
291
43
53.4
13
4.4
0.5
3.5
518.8
0.01
0.03
10.6
1.9
4.2
0.67
3.5
1.17
0.45
1.58
0.28
1.82
0.38
1.15
0.16
1.04
0.15
1.01
1.23
1.02
18.5

Ju323
hornfels
55.86
0.63
13.52
5.01
0.05
2.98
7.51
1.98
5.87
0.16
0.65
0.04
6.10
100.36
2.97
1.41
0.58
54.1
3.79
1.6
184.6
449.3
907
3.1
5.4
145.3
3.9
5.9
0.4
1.1
8.6
<1
32.3
10.3
100
17
78.0
46
9.7
0.5
3.3
264.0
0.41
0.21
24.6
11.8
26.0
3.46
15.2
3.59
0.81
3.71
0.66
3.95
0.78
2.51
0.36
2.48
0.38
0.68
3.21
2.07
75.7

Major- and minor elements in wt. %, trace elements in ppm (except for Au, which is in ppb)

67

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

tion for the assumed granite age of 6 Ma ( 207Pb/206Pb =0.8361 ± 0.0836, i.e., with 10 % uncertainty; Stacey andKramers 1975). It can be demonstrated that variation of
the age of common Pb based on the Stacey–Kramersmodel by several Ma does not have a significant effecton the resulting zircon age calculated for the studied
samples. Regression of data points for samples Ju311
and Ju346 yielded statistically identical U–Pb ages of 6.3± 0.5 and 6.0 ± 0.4 Ma, respectively. However, analysesof zircons from sample Ju328 show variable presence ofinherited component, possibly combined with variable
content of common Pb that does not allow a reliableage calculation.

9. Whole-rock geochemistry

9.1. Major and trace elements
We have analyzed five samples from the felsic suite of the
Guacimal Pluton (Tab. 4) and included three additional
samples published previously by Cigolini and Chaves(1986). The mafic suite is represented by a single analysis(Ju348, Tab. 4) but additional major-element data were
given by Alcorn (1981) with Cigolini and Chaves (1986)
for four and three samples, respectively. Unfortunately,
there is a dearth of high-precision trace-element analyses.
Only Cigolini and Chaves (1986) have presented a handful of trace elements determined by XRF (Cr, Co, Ni, Cu,
Zn, Rb, Sr, Y, Zr, Nb and Ba).

9.1.1. Felsic suite
Despite some textural and modal variation, the felsic
suite shows a remarkable geochemical homogeneity.
Using CIPW normative proportions for plotting the QAP
diagram (Streckeisen 1974) (Fig. 12a), these samples
can be classified as transitional between monzogranites
and granodiorites (SiO2 = 68.8–71.6 wt. %; analyses by
Cigolini and Chaves 1986 reaching up to 75.4 wt. %).
Such a conclusion is in line with the P–Q multicationicplot (Debon and Le Fort 1983; 1988; Fig. 12b), which,however, employs the obsolete term ‘adamellite’, now
discredited by the IUGS. The ternary diagram Na2O –Al2O3 – K2O (mol. %, Fig. 12c) demonstrates that thecontents of both alkalis are roughly balanced (K2O/Na2O= 0.96–1.21 in wt. %).
The rocks are subaluminous as shown by the valuesof Shand’s alumina saturation index, A/CNK (molar
Al2O3/(CaO + Na2O + K2O) uncorrected for apatite) of
0.97–1.03 (Tab. 4; but analyses by Cigolini and Chaves
1986 yield A/CNK values up to 1.13) as demonstrated
also by the multicationic diagram B–A (Debon and Le
Fort 1983; 1988) (Fig. 12d). Additionally, this plot can
68

serve to express the contents of mafic components Fe, Mg
and Ti (= B) and thus the characteristic mineral assemblage. Typical of the felsic suite are low B values, mostly
fulfilling the definition of leucogranitoids (B < 50), andthis, together with the A values oscillating around zero,
points to essentially biotite-bearing assemblages, with,or without, some amphibole. The AFM and SiO2 vs. K2O
diagrams (Figs. 12e–f) document that the felsic suite isclearly high-K calc-alkaline in character (3.4–4.0 wt. %K2O).
The NMORB-normalized spiderplots (Sun and McDonough 1989) for the felsic suite are characterized bya strong enrichment in incompatible elements (RbN =150–167 × NMORB) over the more compatible ones (LuN
= 0.75–1.03 × NMORB) (Fig. 13a). Superimposed are
positive anomalies in Ba, U, K and Pb, as well as troughsin Nb, P and Ti, which are generally considered as typicalof fractionated subduction-related magmas (Pearce andPeate 1995; Tatsumi and Eggins 1995). The total REE
concentrations are rather high, 94.5–134.6 ppm, andthe chondrite-normalized REE patterns (Boynton 1984)
for felsic samples are all subparallel, featuring a strong
LREE/HREE enrichment (LaN/YbN = 5.1–7.1; LaN/SmN= 3.2–4.5; Fig. 13b, Tab. 4), MREE depletion (DyN/YbN< 1, Fig. 14a) and deep negative Eu anomalies (Eu/Eu*= 0.63–0.71 where Eu* = √SmNGdN). The concentrations
Fig. 12 Major-element based diagrams for magmatic rocks of the Guacimal Pluton (for data sources, see the text). a – The QAP diagram (Streckeisen 1974). Instead of modal proportions, CIPW normative compositions are plotted as follows: Q = Quartz (Qz), A = Alkali feldspar (Or),P = Plagioclase (Ab +An); b – Multicationic plot P–Q (Debon and Le
Fort 1983, 1988) (P representing the proportion of K-feldspar to plagioclase and Q the quartz content): gr = granite, ad = adamellite, gd= granodiorite, to = tonalite, sq = quartz syenite, mzq = quartz monzonite, mzdq = quartz monzodiorite, dq = quartz diorite, s = syenite,mz = monzonite, mzgo = monzogabbro, go = gabbro; c – Ternary plot
Na2O – Al2O3 – K2O (mol. %). Dashed lines define the following compositional fields: peraluminous + metaluminous, (Na2O + K2O)/Al2O3< 1; peralkaline, (Na2O + K2O)/Al2O3 > 1; perpotassic, K2O/Al2O3 >1 and K2O/Na2O > 1; potassic, 1 < K2O/Na2O < 3; and ultrapotassic,
K2O/Na2O ≥ 3 in mol. % (or K2O/Na2O ≥ 2 in wt. %, which is equivalent to the definition of ultrapotassic igneous rocks by Foley et al.
1987); d – Multicationic plot B–A (B being proportional to the amountof mafic minerals and A expressing the alumina saturation) (Debon and
Le Fort 1983,1988); e – AFM diagram (A = Na2O + K2O, F = FeOt, M= MgO: Irvine and Baragar 1971) illustrating the calc-alkaline trend
defined by the Guacimal Pluton analyses; f – SiO2–K2O plot (wt. %)with discrimination boundaries between the (low-K) tholeiitic, (medium-K) calc-alkaline, high-K calc-alkaline, and shoshonitic rocks after
Peccerillo and Taylor (1976). The colour fields denote the variation inother Neogene plutonic bodies of Costa Rica (in brackets are references and number of analyses in the database): Talamanca Intrusive Suite (Tournon 1984 – 1, Drummond et al. 1995 – 8, Gräfe 1998 – 41,
Abratis 1998 – 13, Ulloa and Delgado 2010 – 15); Puerto Nuevo Gabbros (Henningsen 1966 – 2, Abratis 1998 – 2); Escazú monzonites–gabbros (Bergoeing 1982 – 2), Guayacan teschenite (Azambre and Tournon 1977 – 4), Desmonte monzogabbro (Tournon 1984 – 1) and Dominical gabbros (Gazel et al. 2009 – 2).

Miocene Guacimal Pluton, Costa Rica
Q

200

250

(b)

ad

gr

150

gd

100

Granodioritetomzdq mzq

sq

50

dq

3

monzonite

go

mzgo

-300

-200

5

mz

s

0

Quartzsyenite
SyeniteMonzogranite

Syenogranite

Q = Si/3-(K+Na+sCa/3)

pg
Alk
ali
Fs
2

Quarz-richgranitoid

e
alit

1

(a)

Ton

ran
ite

1: Qtz-Alkali Fsp syenite
2: Alkali Fsp syenite
3: Qtz monzodiorite
Qtz monzogabbro
4: Monzodiorite
Monzogabbro
5: Qtz diorite
Qtz gabbro
Qtz anorthosite
6: Diorite
GabbroAnorthosite

4

Monzonite

6

A

P

-400

-100

0

-400

P = K - (Na + Ca)

(d)

200

II
Bt > Ms
III
Bt ± ...
IV
Bt ± Amph ±Opx ± Cpx ± ...
V
Cpx ± Amph ± ...

Sodic Potassic

Na2O

0

50

100

200

300

400

500

B = Fe + Mg + Ti

7

F

(e)

(f)
6

Talamanca Intrusive Suite
Puerto Nuevo gabbros
Escazú monzonite-gabbros
Guayacan teschenite
Desmonte monzogabbro
Dominical gabbros

Ultrapotassic
K2O

e

alin

Shoshonite Series

5

Guacimal Granite Pluton
Felsic suite(this work)
Cigolini and Chavez (1986)
Mafic suite(this work)
Alcorn (1981)
Cigolini and Chavez (1986)

-400

Pe

rpo

tas

sic

Peralkaline

Leucogranitoids

Metaluminous
PeraluminousI
Ms > Bt

0

A = Al - (K + Na + 2Ca)

400

(c)

-200

Al2O3

-alk

c
cal

h-K
Hig ies
r
e
S

K 2O

4

Tholeiite Series

ne

2

3

li
-alka
Calc sSerie

1

Tholeiite
Series0

Calc-alkaline Series

A

M

45

50

55

60

65

70

75

SiO 2

69

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

9.2. Sr–Nd isotopes

Granites

50 100

Ju57
Ju98
Ju311
Ju328
Ju346

Qtz diorite

5 10

Ju348

0.5 1

Sample/ NMORB

500
5

Th
Ba

Cs

Nb
U

La
K

Pb
Pr

Ce

Nd

Sr
P

Ti

Sm
Zr

Eu

Y
Dy

Lu
Yb

Talamanca Intrusive Suite(Ulloa and Delgado 2010)

100

0.1

Rb

(Felsic )2050(Mafi c)10

Sample/ REE chondrite

9.1.2. Mafic suite
The mafic rocks are rather variable in composition (SiO2= 45.9–61.2 wt. %), but are all exclusively metaluminous(A/CNK = 0.71–0.95) and sodium-rich (K2O/Na2O =0.27–0.59 wt. %, Tab. 4, see also Fig. 12c–d). In the QAP
and P–Q diagrams (Streckeisen 1974; Debon and Le Fort
1983, 1988), sample Ju348 corresponds to quartz diorite(Fig. 12a–b). The literature data straddle the boundariesof the adjacent quartz monzodiorite/quartz monzogabbro
and tonalite domains (P–Q plot) . However, not all mafic
samples represent liquid compositions; at least some seemto contain a significant proportion of cumulus material
rich in calcic plagioclase and biotite. For instance, thegabbro G12 is very basic and aluminous (SiO2 = 45.92
wt. %, Al2O3 = 21.3 wt. %) and, indeed, this sample shows
as much as 53.9 vol. % of plagioclase (Alcorn 1981). The
degree of fractionation, expressed by mg# [molar 100 ×
MgO/(MgO + FeOt)], is also highly variable (35.5–66.0).
The rocks are mostly normal-K calc-alkaline (K 2O =0.9–1.8 wt. %), with exception of the sample G-5, which
is more potassium-rich (K2O = 2.6 wt. %) (Fig. 12e–f).
The NMORB-normalized pattern of the sample Ju348(Fig. 13a) shows features similar to the felsic suite. Still, it
contains much lower concentrations of LILE (Rb, Ba, U,
Th and K), and the troughs in Ti and P are shallower. On
the other hand, the Nb anomaly is prominent, the LREE
contents are significantly lower (LaN = 28.7 × NMORB)
but the HREE abundances are similar to some members of
the felsic suite (LuN = 0.73 × NMORB). As a consequence,the sample is rather REE poor (Σ REE = 70.6 ppm) and its
chondrite-normalized REE pattern (Fig. 13b) is much flatter, in particular in its LREE segment (LaN/YbN = 2.6; LaN/
SmN = 1.4). The negative Eu anomaly is still significant,but somewhat less conspicuous (Eu/Eu* = 0.81).

(a)

(b)
1

Ce
La

Nd
Pr

Sm

Gd
Eu

Dy
Tb

Er
Ho

Yb
Tm

Lu

Fig. 13 Multielement variation plots (‘spiderplots’) for the Guacimal
Pluton. a – Trace-element values normalized by NMORB (Sun and McDonough 1989). b – Chondrite (Boynton 1984) normalized REE patterns. Colour fields denote the variation in the Talamanca Intrusive Suite (Ulloa and Delgado 2010); pink for its felsic suite (11 monzogranites
and granodiorites) and blue for the mafic suite (3 quartz gabbros/quartz
diorites). The mafic suite of Talamanca has less than 52.2 % SiO2 andits REE patterns do not show a negative Eu anomaly.

70± 24.8 °C (2σ); the temperatures calculated for data by
Cigolini and Chaves (1986) range from 798 to 810 °C.

2

of HREE and Y markedly decrease with increasing silica(e.g., Fig. 14b).
The negative SiO2–Zr correlation (Fig. 14c) for felsic
samples is taken as evidence that zircon saturation wasreached early in the fractionation process (Hoskin et al.
2000; Janoušek 2006). Therefore, the zircon saturation
calculations (Watson and Harrison 1983) were employed
to provide an upper constraint on the liquidus temperatureof the granitic melt (due to possible inheritance). The
obtained median value for the new analyses is 790.7

Whole-rock isotopic ratios for three granites–granodioritesof the Guacimal Pluton are presented in Tab. 5 and plottedin Fig. 15. The Sr and Nd isotopic data are all remarkably uniform (87Sr/86Sr6 ~ 0.70388, ε6Nd ~ +7.4 to +7.6)
and primitive, thus documenting a short crustal residenceof their source (two-stage Nd model ages after Liew and
Hofmann (1988), TNDM
, ranging between 0.196 and 0.213
dGa). The Rb–Sr isotopic compositions would even form acrude linear array (errorchron) with slope corresponding
to an age ~ 7 Ma.

Zr (ppm)

190
170

180

(c)

160

22
20
18

150

0.85

200

Y (ppm)

(b)

24

26

DyN/YbN

(a)

0.90

0.95

1.00

Miocene Guacimal Pluton, Costa Rica

68

69

70

71

SiO2

68

69

70

SiO2

68

71

69

70

71

SiO2

Fig. 14 Binary plots of SiO2 vs. DyN/YbN (normalized to chondritic values of Boynton 1984) Y and Zr for the felsic suite of the Guacimal Pluton.
Tab 5 Sr–Nd isotopic data
SampleRb
Sr 87 86
Rb/ Sr(ppm) (ppm)

JU311
JU328
JU346

88.2 367.7 0.69400 0.703937 0.000012 0.703878 3.46
85.4 348.4 0.70920 0.703942 0.000014 0.703882 3.57
93.7 307.0 0.88306 0.703958 0.000011 0.703883 3.35

87

Sr/86Sr

2 se (m)87

Sr/86Sr6*

Sm
Nd 147
Sm/144Nd 143Nd/144Nd 2 se (m)(ppm) (ppm)
17.3
17.6
19.3

0.120930.122640.10495

0.513025 0.000011
0.513013 0.000008
0.513021 0.000010

Nd/144Nd6* ε6Nd*

TNDM
d0.513020
0.513008
0.513017

0.195
0.213
0.200

143

7.6
7.4
7.5

* Subscripts indicate age to which were isotopic ratios corrected;
epsilon values calculated using Bulk Earth parameters given by Jacobsen and Wasserburg (1980);
TNDM
are two-stage Nd model ages based on Liew and Hofmann (1988)
d

10. Discussion

10.1. Crystallization conditions and age
The granitic rocks of the Guacimal pluton contain primary magmatic assemblage of quartz, plagioclase, K-feldspar, Mg-rich biotite, amphibole, magnetite, and titanite.
The presence of quartz, magnetite and titanite indicates
relatively high oxygen fugacity (Wones 1989). This is
supported by estimates of oxygen fugacity (Ridolfi etal. 2010), which fall in the interval of 1.6–2.1 log units
above the NNO buffer. Together with the geochemical
evidence for plagioclase and biotite accumulation in more
mafic samples, these calculations indicate that the felsic
members of the pluton were emplaced at shallow depthof ~3 km at a relatively high fO2, whereas the mafic rocks
could represent deeper (~ 15 km) cumulates.
The intrusive rocks contain ubiquitous secondary
minerals, which are mostly present in interstitial spacein the rock matrix or as fillings of miarolitic cavities.
They include quartz II, K-feldspar II (adularia), epidote,chlorite (clinochlore), amphibole II (actinolite), ilmenite
II and titanite II. The secondary titanite is extremely richin Al2O3 (5.19–11.26 wt. %) and F (1.46–3.93 wt. %).
The heterovalent substitution of titanium by aluminium
was first recognized by Sahama (1946): Al3+ + (OH, F)–= Ti4+ + O2–. Following Franz and Spear (1984) such amechanism is favoured either by high pressure or low
temperature, in addition to high fluorine activity.
New LA ICP-MS dating of zircons from two granite
samples of the Guacimal Pluton yielded statistically
identical U–Pb ages of 6.3 ± 0.5 and 6.0 ± 0.4 Ma. This
broadly agrees with the K–Ar age on a monzonite (biotite: 3.9 ± 1.0 Ma, alkali feldspar: 5.0 ± 0.2 Ma; Schulz etal. 1987) and a quartz diorite (whole rock: 7.2 ± 1.4 Ma;
Alvarado et al. 1992). The Guacimal Pluton thus ranks
to the youngest Neogene plutonic rocks in Costa Rica,
being comparable in age to the Escazú Pluton (6.3–2.2
Ma), the youngest plutonic member of the Talamanca
Igneous Suite (7.8–3.89 Ma), the Guacayán Intrusion (4.5
Ma) and the Desmonte monzogabbro (2.1 Ma) (all K–Ar
data – Bellon and Tournon 1978; Patino 2007).

10.2. Whole-rock geochemistry
The major-element whole-rock composition of the Guacimal Pluton closely resembles the other Costa Rican
Neogene plutonic rocks, especially the Talamanca Intrusive Suite (Fig 12). This argues for comparable sources
and processes involved in generation of granitic magmas
along the whole (now extinct) arc. However, some intrusive rocks from the back arc (Guayacán teschenite) arealkaline and clearly had different genesis associated totheir likely OIB source (Gazel 2003).

71

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

Arc-related igneous
activity, Costa Rica

Seafloor alterationYdu ojora as)

Mafic suite (literature)

VF
ua
rag

on

Felsic suite (Guacimal)

a
Nic

(H

s,
rce
ou n
d s tio
he inaric m
en ntare l coMo stacru

Felsic suite (literature)

VF
B
ua
g
a
r

Extinct VF (Talamancas)
Adakites
Recent VF
BVF

ca

Ni

Costa Raica VF

BV

ca
Ri
sta

Panam

Y
RA

AR

Co

LE

NT

Galápagos(Harpp andWhite 2001)

Cocos Ridge(Sadofsky et al. 2009)MA

La
Providencia(Colombia)

F

Costa Ri
Rica extVF
Ric

Fig. 15 Present-day Sr–Nd isotopic diagram for the pre-Quaternary felsic and mafic intrusive rocks of Costa Rica (seven diorites of Gräfe 1998,
tholeiitic gabbro INA-84 and calc-alkaline monzodiorite ALT 95 from Abratis 1998, and this work). The context is provided by analyses of arc-related igneous rocks from Costa Rica: extinct volcanic front (VF) and adakites in Cordillera de Talamanca, recent VF in western Costa Rica andrelated behind-volcanic front (BVF) volcanism (Abratis 1998; Feigenson et al. 2004). For comparison, shown are also the fields of the Central
American Volcanic Arc (CAVA) data from the neighbouring countries – recent/extinct VF and BVF lavas in Nicaragua, VF lavas in Panama and
BVF lavas from Colombian Isla de Providencia (Feigenson et al. 2004; Janoušek et al. 2010). Also plotted are fields of Yojoa BVF lavas derived
from an OIB-like source in back-arc setting in Honduras (Feigenson et al. 2004), Galápagos lavas (Harpp and White 2001) and Cocos Ridge analyses (Sadofsky et al. 2009). Gray field indicates approximate extent of the Mantle Array.

The trace-element compositions of the Guacimal intrusive suite are well within the range of the Talamanca
Intrusive Suite (Fig 13), the former only show more
pronounced Eu anomalies. Vogel et al. (2004) pointed
out that the trace-element distribution in the Costa Rican
silicic ignimbrites resembles that in the plutonic rocks(granites and granodiorites of the Talamanca Intrusive
72

Suite; Drummond et al. 1995; Abratis 1998). Moreover,
it is close to the composition of the average upper continental crust, a conclusion valid for the Guacimal samples
as well.
The rocks of the felsic Guacimal suite show only moderate negative Eu anomalies accompanied by a marked
depletion in MREE (e.g., low DyN/YbN = 0.83–0.94), cor-

Miocene Guacimal Pluton, Costa Rica

responding to the low-temperature, hydrous and oxidized
suite of high-SiO2 rhyolites as defined by Bachmann
and Bergantz (2008). This is in agreement with rather
low estimated temperatures of magmatic crystallization(c. 760–800 °C). The observed MREE depletion is in linewith an important role of amphibole and/or titanite either
in the residue after melting, or, more likely, in the fractionating assemblage (Gromet and Silver 1983; Tiepolo
et al. 2002, 2007; Davidson et al. 2007).

10.3. Sr–Nd isotopes
As shown in Fig. 15, the Sr–Nd isotopic signatures for
the Guacimal granites–granodiorites form a rather tightcluster slightly off to the right of the Mantle Array.
When compared with the subduction-related Costa Rican
volcanic rocks, they fall into the most primitive (low87
Sr/86Sr, high 143Nd/144Nd) corner of the field occupiedby the analyses from the extinct Cordillera de Talamanca
volcanic front; they also coincide with the top (mostradiogenic Nd) part of the nearly vertical isotopic dataarray for the recent volcanic arc, including most of thesilicic ignimbrites (see “trend 1” in fig. 23.8 of Vogel etal. 2007). On the other hand, they definitely have lessradiogenic Nd and more radiogenic Sr than the current
behind-volcanic front (BVF) volcanics of the same arc.
The Sr–Nd isotopic compositions of the Guacimal Pluton,
however, compare particularly well with the previously
determined data (87Sr/86Sr6 = 0.70380–0.70413, ε6Nd ~ +7.3
to +7.9) from Neogene intermediate–acid calc-alkaline
plutonic rocks from Costa Rica (tonalite to alkali granite
samples CHI 116, INA 85, TAL 79 and 19 of Abratis
1998 and Gräfe 1998).

10.4. Magma source and evolution
In the Guacimal Pluton, the homogeneous Sr–Nd isotopic
compositions exclude open-system processes such as contamination by evolved continental crust or magma mixing
between primitive, mantle-derived melts and magmas
generated by anatexis of isotopically contrasting continental crust (see also Vogel et al. 2004). The available
data for the extinct arc in Cordillera de Talamanca (sevendiorites of Gräfe 1998, tholeiitic gabbro INA-84 and calcalkaline monzodiorite ALT 95 from Abratis 1998) span
identical range as the Guacimal suite does in both Nd (ε6Nd~ +7.2 to +8.0) and Sr (87Sr/86Sr6 = 0.70381–0.70389),
and this appears to support the origin by differentiation
in a closed system.
The observed slight shift to the more radiogenic Sr(right from the Mantle Array) in intrusive rocks, including the Guacimal Pluton, probably reflects a role ofhydrous, subduction-related fluids that tend to be rather
Sr-rich but Nd-poor (Feigenson and Carr 1986). As dis-cussed by Janoušek et al. (2010), subducted metabasic
rocks of the Cocos Plate should have significantly elevated Sr isotopic ratios due to the seawater alteration,and this is indeed shown by the analyses of the Galápagos-influenced ocean-floor lavas (Sadofsky et al. 2009)(Fig. 15). Such an effect is even more clearly seen in
the recent Nicaraguan volcanic-front lavas, which are,in particular in the NW Nicaragua, thought to have been
derived from a strongly depleted mantle wedge (Carret al. 2007 and references therein; Hoernle et al. 2008;
Sadofsky et al. 2009).
As there are only very limited reliable data for themafic rocks, we shall exclusively focus on the felsic
suite. Its rather homogeneous, radiogenic Nd and fairly
unradiogenic Sr isotopic signatures require: (1) partial
melting of young, immature metaigneous crust (including
a subrecent basic magma underplate, which is believed
to form near the Moho level of long-lived igneous arcs
– Atherton and Petford 1993), or (2) direct fractionationfrom fairly depleted mantle-derived magmas (see also
Vogel et al. 2004, 2006).
The presence of marked negative Eu anomalies in the
Guacimal granitic rocks would be compatible with ananatexis of a feldspar-rich source, leaving much of thismineral in the residue. The CaO/Na2O ratios in anatectic
magmas are controlled mostly by the protolith’s plagioclase/clay ratio (Sylvester 1998; Jung and Pfänder 2007).
The felsic suite is characterized by high CaO/Na2O ratios(0.62–0.76; Tab. 4), pointing to mainly a plagioclase-rich,and thus not metapelitic, source. Such a conclusion is inline with the subaluminous nature, as well as low Rb/Sr
and Rb/Ba ratios of the Guacimal granites (Harris andInger 1992; Tab. 4). In addition, in the binary plot Al2O3+ FeOt + MgO + TiO2 vs. Al2O3/(FeOt + MgO + TiO2) ofJung et al. (2009) the felsic Guacimal samples fall clearly
into a domain occupied by experimental melts of intermediate metaigneous or metapsammitic parentage (Fig. 16).
Roberts and Clemens (1993) as well Sisson et al.
(2005) concluded, based on experimental data, that thehigh-K calc-alkaline granitic magmas – such as thosein Guacimal Pluton – may be derived exclusively byintracrustal partial melting of hydrous, calc-alkaline tohigh-K calc-alkaline, mafic to intermediate metaigneousrocks. The modal composition of the Guacimal granitic
rocks rules out partial melting of common K-poor metabasites as it should lead to tonalitic–trondhjemitic andnot granodioritic–granitic melts (e.g., Wolf and Wyllie
1994; Rapp and Watson 1995; Johannes and Holtz 1996).
On the same basis can be effectively discounted themodel of Atherton and Petford (1993) invoking remelting of the deep crustal metabasic underplate. Moreover,the magmas parental to the Guacimal granitoids wereapparently too cold to have formed by dehydration melting of amphibole at reasonable depths (e.g., Miller et al.
73

25

30

Al2O3/(FeOt + MgO + TiO2)

35

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

10

15

20

Pelite-derived melts

5

Greywacke-derived melts

0

Amphibolite d.m.
0

10

20

30

40

50

Al2O3 + FeOt + MgO + TiO2
Fig. 16 Binary plot of Al2O3 + FeOt + MgO + TiO2 vs. Al2O3/(FeOt+ MgO + TiO2); outlined are domains occupied by experimental granitic melts obtained by partial melting of metapelites, metagreywackes and amphibolites (experiments of Patiño Douce 1999 as summarised by Jung et al. 2009). Within the Guacimal Pluton suite, the mafic
group clearly requires a metabasic source, while the felsic rocks could
be derived from intermediate metaigneous or metapsammitic sources.

2003). If true, the partial melting model would require a
K-rich, rather young, intermediate metaigneous source,that is volcanics, volcaniclastics or immature graywackes,
rich in the arc-derived volcanogenic detritus. All such
lithologies would be characterized by primitive Sr–Nd
isotopic composition and time-integrated low Rb/Sr andhigh Sm/Nd ratios.
The hypothesis involving closed-system fractionationfrom primary, mantle-derived magmas, however, remains to be tested. Were all rock types in the Guacimal
Pluton a part of a single ‘line of descent’ from primary,mantle-derived magmas, one would expect to encounter

large volumes of mafic cumulates and increasingly lessabundant products of the magma differentiation. In reality, the distribution is close to bimodal, with the bulk of
the intrusion being built by the felsic types. The mafic
rocks are rather rare, forming only infrequent, small
discrete bodies. Moreover, there is conspicuous discontinuity in the geochemical trends (e.g., the SiO 2 – K2O
plot, Fig. 12f or the REE patterns, Fig. 13b). This reasoning is valid only for conventional models of crystal
fractionation, whereby the individual crystals or theirclusters separate from prevailing melt, though. Basedon Bachmann and Bergantz (2004), Vogel et al. (2004,
2006, 2007) proposed an alternative scenario for genesisof the silicic ignimbrites in Costa Rica. In their view,
the parental silicic magmas represent limited amountsof fractionated liquid squeezed out from lower crustal
crystal mush (containing ~ 50–60 % of crystals according to Bachmann and Bergantz 2008), mainly amphibole
and plagioclase, along with lesser amounts of pyroxene(Vogel et al. 2007).
In order to test the prospective role of fractional crystallization in genesis of the felsic suite, constrained leastsquares method (Albarède 1995) has been applied to themajor-element analyses using an unpublished R language
routine written for the GCDkit (Janoušek et al. 2006). The
input data were the composition of the most primitive(parental) melt (the least siliceous sample Ju98), that ofthe presumed residual magma (the most SiO2-rich sample
Ju346) and those of the likely crystallizing mineral phases. The model took into account SiO2, Al2O3, FeOt, MnO,
MgO, CaO, Na2O and K2O. The calculation suggests thatthe compositional spectrum of the felsic suite can be reproduced by limited fractionation (~15 %) of 54.9 % Pl,
22.4 % Kfs, 9.2 % Hbl, 8.1 % Bt and 5.4 % Mgt (Tab. 6).
The fit is good, as indicated by the low value of the sumof squared residuals (R2 = 0.23). Moreover, the calculated
cumulate composition falls within the compositional
range known from the mafic suite.

Tab 6 Least-squares modelling of fractional crystallization
15.1% fractional crystallization of (wt. %)Parent
54.9%
22.4%
Ju98
Pl
Kfs
SiO2
68.83
60.46
63.42
TiO2
0.43
0.00
0.00
Al2O3
14.91
24.01
18.79
FeOt
2.72
0.38
0.13
MnO
0.11
0.00
0.00
MgO
0.77
0.00
0.00
CaO
2.44
5.98
0.09
Na2O
3.56
8.12
1.98
K 2O
3.86
0.64
13.19

9.2%
Hbl
41.12
2.30
12.22
11.69
0.18
14.33
11.55
2.51
0.46

8.1%
Bt
38.25
4.16
12.80
12.30
0.12
17.64
0.00
0.51
9.28

5.4%
Mgt
0.01
0.31
0.13
94.25
0.11
0.00
0.04
0.02
0.00

Daughter
Ju346
71.55
0.29
14.15
2.03
0.10
0.64
2.21
3.55
4.00

Calculated
71.41
0.41
14.09
1.89
0.12
0.42
2.10
3.27
3.82
R2 = 0.230

74

Difference
0.14
-0.12
0.06
0.14
-0.02
0.22
0.11
0.28
0.18

Cumulate
54.30
0.57
19.56
7.37
0.03
2.75
4.37
5.17
4.10

Miocene Guacimal Pluton, Costa Rica

11. Conclusions
The Guacimal Pluton forms an oval-shaped body (~15
by 4–6 km), strongly elongated in the NW–SE direction.
By its exposed surface of 60–70 km2 it represents thelargest plutonic mass in the NW Costa Rica. The pluton
intruded the Aguacate Group and is surrounded by awide metasomatic aureole of calc-silicate rocks, derived
from mafic volcanics. The pluton is formed by a felsic(granite–granodiorite) and a mafic suite (mainly quartz
diorite to quartz monzodiorite/monzogabbro); the former
strongly prevails.
The new LA ICP-MS zircon dating from granites
yielded statistically identical U–Pb ages of 6.3 ± 0.5 and
6.0 ± 0.4 Ma. The late Miocene Guacimal granites thus
belong to one of the youngest Neogene intrusions in
Costa Rica, together with the Escazú Pluton, the youngest
plutonic members of the Talamanca Igneous Suite and
the Guacayán Intrusion.
Based on amphibole geobarometry, the emplacement
depth of the Guacimal Pluton was approximately 3 km.
Such a shallow solidification level is also supported by
the occurrence of micrographic structures and abundantmiarolitic cavities. The near solidus crystallization temperatures of c. 760–800 °C were estimated by plagioclase–amphibole and zircon saturation thermometers. The
presence of the assemblage quartz, magnetite, titanite,
and Mg-rich amphibole indicates a relatively high oxygen
fugacity, 1.6–2.1 log units above the NNO buffer. Duringsolidification, high Al and F contents in titanite and thepresence of epidote and chlorite in miarolitic cavities document increasing activity of volatiles (fluorine and water).
The Sr–Nd isotopic signatures of the Guacimal monzogranites and granodiorites are primitive and show
only very limited variation, which precludes for opensystem processes such as magma mixing or assimilationof isotopically contrasting upper continental crust. The
conventional extensive fractionation of depleted-mantle
derived magmas is considered unlikely, as it would
produce only relatively small volume of felsic magmas
and large amounts of cumulates, for presence of which
any evidence is lacking. Instead the Sr–Nd isotopic data,
together with the rest of the whole-rock geochemicalsignature, indicate either crystallization from a highly
fractionated melt separated from a plagioclase–amphibole-dominated crystal mush in a putative deep crustal
reservoir, or partial melting of older arc-related rocks (seethe characteristic LILE/HFSE enrichments as well as theslight shift to more radiogenic 87Sr/86Sr ratios caused byslab-derived fluids). If true, the latter scenario would require a source with relatively unradiogenic Sr, radiogenic
Nd, low time-integrated Rb/Sr and comparably high Sm/
Nd ratios and thus could have encompassed intermediatelavas or volcaniclastics or immature psammitic sedi-ments, such as graywackes rich in volcanogenic detritus.
Limited variation observed in the felsic suite was most
likely produced by low degrees (~15 %) of closed-systemfractional crystallization of an assemblage dominated byfeldspars (c. 55 % plagioclase, 23 % K-feldspar, 9 %amphibole, 8 % biotite and 5 % magnetite). At least
some of the rocks of the volumetrically subordinate mafic
suite may represent lithologies rich in the complementary
cumulates.
Acknowledgements. This paper resulted from the International project No RP/6/2007 of Ministry of Environmentof the Czech Republic, which was led by Petr Hradecký
and Petr Kycl. The fieldwork was carried out by geologists of the Czech Geological Survey (CGS) in cooperation with the Department of Geology and Mines (DGM)of Ministry of Environment, Energy and Telecommunications of Costa Rica (MINAET) in 2006–2009. In the fieldworks (sheet Juntas) participated also other colleagues
from both Czech Republic and Costa Rica: Stanislav
Čech, Barbora Dudík Schulmannová, Gino Gonzales,
Radek Grygar, Petr Hrazdíra, Jana Karenová, Petr Lukeš,
Enrique Quintanilla, Josef Ševčík, and Tomáš Vorel. The
authors are also obliged to Radek Škoda, Masaryk University Brno, for obtaining electron microprobe analyses,
František Laufek and Irena Haladová (CGS) for acquiring
XRD data and František Veselovský (CGS) for separation of zircons for dating. The reviewers, Thomas Vogeland Lawford Anderson, as well as handling editor David
Dolejš, provided helpful comments on the manuscript that
improved its quality.
Electronic supplementary material. The GPS coordinatesof the analysed samples, as well as selected mineral analyses of feldspars (Appendix 1), biotite and orthopyroxene(Appendix 2), magnetite (Appendix 3), ilmenite (Appendix 4), titanite (Appendix 5) and epidote-group minerals
with prehnite (Appendix 6) are available online at the
Journal web site (http://dx.doi.org/10.3190/jgeosci.087).

References
Abratis M (1998) Geochemical Variations in MagmaticRocks from Southern Costa Rica as a Consequence of
Cocos Ridge Subduction and Uplift of the Cordillera deTalamanca. Unpublished PhD. Thesis, Georg–August–
Universität, Göttingen, pp 1–148
Albarède F (1995) Introduction to Geochemical Modeling.
Cambridge University Press, Cambridge, pp 1–543
Alcorn SR (1981) Mineralogy, Petrology and Evolution of
a Calc-Alkaline Igneous Sequence, Cerros de Tilarán,
Puntarenas, Costa Rica. Unpublished MSci. Thesis,
University of Georgia, Athens, pp 1–178
75

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

Alvarado GE, Kussmaul S, Chiesa S, Gillot P-Y, Appel
H, Wörner G, Rundle C (1992) Resumen cronoestratigráfico de las rocas ígneas de Costa Rica basado en
dataciónes radiométricas. J South Am Sci 6: 151–168
Alvarado GE, Denyer P, Sinton CW (1997) The 89 Ma
Tortugal komatiitic suite, Costa Rica: implications
for a common geological origin of the Caribbean andEastern Pacific region from a mantle plume. Geology
25: 439–442
Amos BJ, Rogers PJ (1983) The geology and exploration
geochemistry of the Cordillera Tilarán – Montes delAguacate gold field, Costa Rica. British Geological Survey, Institute of Geological Sciences, Overseas Division,
Open-File Report No 1983/3, pp 1–33
Anderson JL (1996) Status of thermobarometry in granitic
batholiths. Trans Roy Soc Edinb, Earth Sci 87: 25–138
Anderson JL Smith DR (1995) The effects of temperatureand f02 on the Al-in-hornblende barometer. Amer Miner
80: 549–559
Appel H (1990) Geochemie und K–Ar Datierungen an
Magmatiten in Costa Rica, Zentralamerika. UnpublishedMSci. Thesis, University of Mainz, pp 1–149
Astorga A (1987) El Cretácico Superior y el Paleógeno dela vertiente pacifica de Nicaragua meridional y Costa
Rica septentrional: origen, evoluticón y dinámica de lascuencas profundas relacionadas al margen convergente
de Centroamérica. Unpublished MSci. Thesis, Univesidad de Costa Rica, San José, pp 1–115
Atherton M, Petford N (1993) Generation of sodium-richmagmas from newly underplated basaltic crust. Nature
362: 144–146
Azambre B, Tournon J (1977) Les intrusions basiques
alcalines du Río Reventazon (Costa Rica). C R Somm
Soc Geol Fr 2: 104–107
Bachmann O, Bergantz G W (2004) On the origin of
crystal-poor rhyolites: extracted from batholithic crystal
mushes. J Petrol 45: 1565-1582
Bachmann O, Bergantz GW (2008) Rhyolites and theirsource mushes across tectonic settings. J Petrol 49:
2277–2285
Baumgartner PO, Denyer P (2006) Evidence for middle
Cretaceous accretion at Santa Elena Peninsula (Santa
Rosa Accretionary Complex), Costa Rica. Geol Acta
4: 179–191
Bellon H, Tournon J (1978) Contribution de la géochronometrie K–Ar a l‘étude du magmatisme de Costa Rica,
Amérique Central. Bull Soc Geol de France 20: 955–959
Bergoeing JP (1982) Dataciones radiométricas de algunas
muestras de Costa Rica. Instituto Geográfico Nacional
Informe Semestral enero–diciembre 28: 71–86
Boynton WV (1984) Cosmochemistry of the rare earth
elements: meteorite studies. In: Henderson P (ed) Rare
Earth Element Geochemistry. Elsevier, Amsterdam, pp
63–11476

Carr MJ, Patino LC, Feigenson MD (2007) Petrology andgeochemistry of lavas. In: Bundschuh J, Alvarado GE(eds) Central America: Geology, Resources and Hazards.
Taylor & Francis, London, pp 565–590
Chaves R, Sáenz R (1974) Geología de Cordillera de Tilarán(proyecto de Aguacate, 2a Fase). Costa Rica, Dirección deGeología, Minas y Petróleo, Informes Técnicos y Notas
Geológicas 12(53): 1–49
Cigolini C, Chaves R (1986) Geological, petrochemical
and metallogenetic characteristics of the Costa Rican
gold belt: contribution to new exploration. Geol Rundsch
75: 737–754
Corfu F, Hanchar JM, Hoskin PWO, Kinny P (2003) Atlasof zircon textures. In: Hanchar JM, Hoskin PWO (eds)
Zircon. Mineralogical Society of America and Geochemical Society Reviews in Mineralogy and Geochemistry53: 469–503
Davidson J, Turner S, Handley H, Macpherson C, Dosseto
A (2007) Amphibole “sponge” in arc crust? Geology
35: 787–790
De Boer JZ, Drummond M, Bordelon M, Defand M, Bellon H, Maury R (1995) Cenozoic magmatic phasesof the C. R. island arc (Cordillera de Talamanca). In:
Mann P (ed) Geologic and Tectonic Development of the
Caribbean Plate Boundary in Southern Central America.
Geological Society America Special Papers 295: 35–55
Debon F, Le Fort P (1983) A chemical–mineralogical classification of common plutonic rocks and associations.
Trans Roy Soc Edinb, Earth Sci 73: 135–149
Debon F, Le Fort P (1988) A cationic classification of common plutonic rocks and their magmatic associations:principles, method, applications. Bull Minéral 111:
493–510
Dengo G (1962) Tectonic–igneous sequence in Costa Rica.
In: Engel AEJ, James HJ, Leonard BF (eds) Petrologic
Studies. A volume to honor A. F. Buddington. GeologicalSociety of America, New York, pp 133–161
Denyer P, Alvarado GE (2007) Mapa Geológico de Costa
Rica 2007. Libreria Francesa, San José
Denyer P, Arias O (1991) Estratigrafia de la región central
de Costa Rica. Rev geol Amer Central 12: 1–59
Denyer P, Baumgartner PO, Gazel E (2006) Characterization and tectonic implications of Mesozoic–Cenozoic
oceanic assemblages of Costa Rica and Western Panama.
Geol Acta 4: 219–235
Donelly TW, Beets D, Carr MJ, Jackson T, Klaver G,
Lewis J, Maury R, Schellkens H, Smith AL, Wadge G,
Westercamp D (1990) History and tectonic setting of
Caribbean magmatism. In: Dengo G, Case J (eds) The
Geology of North America, Volume H – The Caribbean
Region. Geological Society of America, Boulder (CO),pp 339–374
Drummond MS, Bordelon M, De Boer J, Defant MJ,
Bellon H, Feigenson MD (1995) Igneous petrogenesis

Miocene Guacimal Pluton, Costa Rica

and tectonic settings of plutonic and volcanic rocks of
Cordillera de Talamanca, Costa Rica–Panama, Central
American Arc. Amer J Sci 295: 875–919
Dunstan LP, Gramlich JW, Barnes IL, Purdy WC (1980)
The absolute abundance and the atomic weight of a reference sample of thallium. J Res Natl Bur Stand 85: 1–10
Feigenson MD, Carr MJ (1986) Positively correlated Ndand Sr isotope ratios of lavas from the Central American
volcanic front. Geology 14: 79–92
Feigenson MD, Carr MJ, Maharaj SV, Juliano S, Bolge
LL (2004) Lead isotope composition of central American
volcanoes: influence of the Galapagos plume. Geochem
Geophys Geosyst 5: DOI: 10.1029/2003GC000621
Foley SF, Venturelli G, Green DH, Toscani L (1987)
Ultrapotassic rocks: characteristics, classification andconstraints for petrogenetic models. Earth Sci Rev 24:
81–134Franz G, Spear FS (1984) Aluminous titanite (sphene) fromthe Eclogite Zone, south-central Tauern Window, Austria.
Chem Geol 50: 33–46
Gans PP, MacMillan I, Alvarado GE, Pérez W, Sigarán
C (2002) Neogene evolution of the Costa Rican Arc.
Geological Society of America Abstracts with Programs
34(6): 513
Gans PP, Alvarado GE, Perez W, MacMillan I, Calvert
A (2003) Neogene evolution of the Costa Rican Arc
and development of the Cordillera Central. GeologicalSociety of America Abstracts with Programs 35(4): 74
Gazel E (2003) Las series alcalinas del Plioceno de Costa
Rica: distribución espacial y relación con una fuente
mantélica tipo OIB. Rev geol Amer Central 29: 87–93
Gazel E, Carr M, Hoernle K, Feigenson MD, Szymanski
D, Hauff F, Bogaard P (2009) Galapagos-OIB signature
in southern Central America: mantle refertilization byarc–hot spot interaction. Geochem Geophys Geosyst 10:
DOI: 10.1029/2008GC002246
Gillot P-Y, Chiesa S, Alvarado GE (1994) Chronostratigraphy of upper Miocene–Quaternary volcanism innorthern Costa Rica. Rev geol Amer Central 17: 45–53
Gräfe K (1998) Exhumation and thermal evolution of theCordillera de Talamanca (Costa Rica): constraints fromfission track analysis, 40Ar–39Ar, and 87Rb–87Sr chronology. Tübinger Geowiss Arb A39: 1–113
Gromet LP, Silver LT (1983) Rare earth element distribution among minerals in a granodiorite and theirpetrogenetic implications. Geochim Cosmochim Acta
47: 925–939
Harpp KS, White WM (2001) Tracing a mantle plume:
isotopic and trace element variations of Galápagos
seamounts. Geochem Geophys Geosyst 2: DOI:
10.1029/2000GC000137
Harris N B W, Inger S (1992) Trace element modellingof pelite-derived granites. Contrib Mineral Petrol 110:
46–56

Henningsen D (1966) Die pazifische Küstenkordillere(Cordillera Costeña) Costa Ricas und ihre Stellung innerhalb des südzentralamerikanischen Gebirges. Geotekt
Forsch 23: 3–66
Hoernle K, Abt DL, Fischer KM, Nichols H, Hauff F,
Abers G A, van den Bogaard P, Heydolph K, Alvarado
G, Protti M, Strauch W (2008) Arc-parallel flow in the
mantle wedge beneath Costa Rica and Nicaragua. Nature
451: 1094–1097
Holland TJB, Blundy JD (1994) Non-ideal interactions
in calcic amphiboles and their bearing on amphibole–plagioclase thermometry. Contrib Mineral Petrol 116:
433–447
Horn I, Rudnick RL, McDonough WF (2000) Precise
elemental and isotope ratio measurement by simultaneous solution nebulisation and laser ablation-ICP-MS:
application to U–Pb geochronology. Chem Geol 164:281–301
Hoskin PWO, Kinny PD, Wyborn D, Chappell BW (2000)
Identifying accessory mineral saturation during differentiation in granitoid magmas: an integral approach.
J Petrol 41: 1365–1396
Irvine TN, Baragar WRA (1971) A guide to the chemicalclassification of the common volcanic rocks. Can J EarthSci 8: 523–548
Jackson SE, Pearson NJ, Griffin WL, Belousova EA(2004) The application of laser ablation-inductively
coupled plasma-mass spectrometry to in situ U–Pb zircon
geochronology. Chem Geol 211: 47–69
Jacobsen SB, Wasserburg GJ (1980) Sm–Nd isotopic evolution of chondrites. Earth Planet Sci Lett 50: 139–155
Janoušek V (2006) Saturnin, R language script for application of accessory-mineral saturation models in igneous
geochemistry. Geol Carpath 57: 131–142
Janoušek V, Farrow CM, Erban V (2006) Interpretation ofwhole-rock geochemical data in igneous geochemistry:
introducing Geochemical Data Toolkit (GCDkit). J Petrol
47: 1255–1259
Janoušek V, Erban V, Holub FV, Magna T, Bellon H,
Mlčoch B, Wiechert U, Rapprich V (2010) Geochemistry and genesis of behind-arc basaltic lavas from eastern
Nicaragua. J Volcanol Geotherm Res 192: 232–256
Johannes W, Holtz F (1996) Petrogenesis and Experimental Petrology of Granitic Rocks. Springer, Berlin,
pp 1–335
Jung S, Pfänder JA (2007) Source composition and melting
temperatures of orogenic granitoids: constraints from
CaO/Na2O, Al2O3/TiO2 and accessory mineral saturation
thermometry. Eur J Mineral 19: 859–870
Jung S, Masberg P, Mihm D, Hoernes S (2009) Partial
melting of diverse crustal sources – constraints from
Sr–Nd–O isotope compositions of quartz diorite–granodiorite–leucogranite associations (Kaoko Belt, Namibia).
Lithos 111: 236–251
77

Vladimír Žáček, Vojtěch Janoušek, Andrés Ulloa, Jan Košler, Sofia Huapaya, Petr Mixa, Lenka Vondrovicová, Guillermo E. Alvarado

Kessler SE, Sutter JF, Issogonis MJ, Jones LM, Walker
RL (1977) Evolution of porphyry copper mineralizationin Ocean Island Arc: Panama. Econ Geol 72: 1142–1153
Košler J, Sylvester PJ (2003) Present trends and the futureof zircon in geochronology: laser ablation ICPMS. In:
Hanchar JM, Hoskin PWO (eds) Zircon. MineralogicalSociety of America and Geochemical Society Reviewsin Mineralogy and Geochemistry 53: 243–275
Košler J, Fonneland H, Sylvester PJ, Tubrett M, Pedersen
RB (2002) U–Pb dating of detrital zircons for sedimentprovenance studies – a comparison of laser ablation
ICPMS and SIMS techniques. Chem Geol 182: 605–618
Kretz R (1983) Symbols for rock-forming minerals. Amer
Miner 68: 277–279
Kussmaul S (1987) Petrología de las rocas intrusivas neogenas de Costa Rica. Rev geol Amer Central 7: 83–111
Kussmaul S (2006) Estratigrafía de las rocas ígneas In:
Denyer P, Kussmaul S (eds) Geología de Costa Rica.
Instituto Tecnológico de Costa Rica, San José, pp 63–86
Kussmaul S, Tournon J, Alvarado GE (1994) Evolutionof the Neogene to Quaternary igneous rocks of Costa
Rica. Profil 7: 97–123
Kycl P, Žáček V, Čech S, Grygar R, Hrazdíra P, Huapaya
S, Karenová J, Kondrová L, Mendoza EQ, Metelka
V, Mixa P, Ševčík J, Vorel T, Hradecká L, Rejchrt
M, Švábenická L (2010) Estudio geológico, informe
final (2006–2009): hojas 3246 II – Miramar, 3246 III –Chapernal, 3246 IV – Juntas, Costa Rica. Unpublishedmanuscript, Czech Geological Survey, Prague and DGM,
San José, pp 1–263
Laguna MJ (1983) Hydrothermale Veänderung und Verwitterungseffekte in Vulkaniten der Aguacate Formacion(Miozän, Pliozän), Costa Rica, Zentralamerika. Zbl Geol
Paläont 1: 223–233
Laguna MJ (1984) Efectos de alteración hidrotermal y
meteorización en volcanitas del Grupo Aguacate, Costa
Rica. Rev geol Amer Central 1: 1–18
Leake BE, Wooley AR, Arps CES, Birch WD, Gilbert MC,
Grice JD, Hawthorne FC, Kato A, Kisch HJ, Krivovichev VG, Linthout K, Laird J, Mandarino J, Maresch
WV, Nickel EH, Rock NMS, Schumacher JC, Smith JC,
Stephenson NCN, Whittaker EJW, Youzhi G (1997)
Nomenclature of amphiboles: Report of the Subcommittee on Amphiboles of the International Mineralogical
Association Commission on New Minerals and Mineral
Names. Mineral Mag 61: 295–321
Liew TC, Hofmann AW (1988) Precambrian crustal components, plutonic associations, plate environment of the Hercynian Fold Belt of Central Europe: indications from a Nd
and Sr isotopic study. Contrib Mineral Petrol 98: 129–138
Ludwig KR (1999) IsoplotEx v. 2.6. Berkeley Geochronological Center Special Publications 1a: 1–50
MacMillan I, Gans PB, Alvarado G (2004) Middle Miocene to present plate tectonic history of the southern
78

Central American Volcanic Arc. Tectonophysics 392:
325–348
Míková J, Denková P (2007) Modified chromatographic
separation scheme for Sr and Nd isotope analysis ingeological silicate samples. J Geosci 52: 221–226
Miller CF, McDowell SM, Mapes RW (2003) Hot and cold
granites? Implications of zircon saturation temperaturesand preservation of inheritance. Geology 31: 529–532
Ondruš P, Skála R (2004) ZDS–WX Search/Match. A computer program
Otten MT (1984) The origin of brown hornblende in the
Artfjället gabbro and dolerites. Contrib Mineral Petrol
86: 189–199
Patino LC (2007) Intrusive rocks. In: Bundschuh J, Alvarado GE (eds) Central America: Geology, Resources,
Hazards, vol 1. Taylor and Francis, London, pp 549–564
Patiño Douce AE (1999) What do experiments tell us about
relative contributions of crust and mantle to the origin of
granitic magmas? In: Castro A, Fernández C, Vigneresse JL (eds) Understanding Granites: Integrating New
and Classical Techniques. Geological Society of London
Special Publications 168: 55–75
Peccerillo A, Taylor SR (1976) Geochemistry of Eocene
calc-alkaline volcanic rocks from the Kastamonu area,
Northern Turkey. Contrib Mineral Petrol 58: 63–81
Pearce JA, Peate DW (1995) Tectonic implications of thecomposition of volcanic arc magmas. Ann Rev Earth
Planet Sci 23: 251–285
Pin C, Zalduegui JFS (1997) Sequential separation oflight rare-earth elements, thorium and uranium by
miniaturized extraction chromatography: application
to isotopic analyses of silicate rocks. Anal Chim Acta
339: 79–89
Pin C, Briot D, Bassin C, Poitrasson F (1994) Concomitant separation of strontium and samarium-neodymiumfor isotopic analysis in silicate samples, based on specific extraction chromatography. Anal Chim Acta 298:
209–217
Pouchou JL, Pichoir F (1985) ‘PAP’ (φ–ρ–Z) correction
procedure for improved quantitative microanalysis. In:
Armstrong JT (ed) Microbeam Analysis. San Francisco
Press, pp 104–106
Rapp RP, Watson EB (1995) Dehydration melting of metabasalt at 8–32 kbar: implications for continental growthand crust-mantle recycling. J Petrol 36: 891–931
Ridolfi F, Renzulli A, Puerini M (2010) Stability andchemical equilibrium of amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations
and application to subduction-related volcanoes. Contrib
Mineral Petrol 160: 45–66
Roberts MP, Clemens JD (1993) Origin of high-potassium,
calc-alkaline, I-type granitoids. Geology 21: 825–828
Sadofsky S, Hoernle K, Duggen S, Hauff F, Werner R,
Garbe–Schönberg D (2009) Geochemical variations inMiocene Guacimal Pluton, Costa Rica

the Cocos Plate subducting beneath Central America:
implications for the composition of arc volcanism and theextent of the Galápagos hotspot influence on the Cocos
oceanic crust. Int J Earth Sci 98: 901–913
Sahama TG (1946) On the chemistry of the mineral titanite.
C R Soc Geol Finlande 138: 88–122
Schulz K, Koeppen R, Ludington S, Kussmaul S, Gray
K (1987) Volcanological framework for the gold
deposits in the Cordillera de Tilarán and Montes delAguacate, Costa Rica. In: Mineral Resource Assessment of the Republic of Costa Rica (USGS–DGMP–
UCR). USGS Miscellaneous Investigation Series Map
1-1865: 34–75
Sisson TW, Ratajeski K, Hankins WB, Glazner AF (2005)
Voluminous granitic magmas from common basaltic
sources. Contrib Mineral Petrol 148: 635–661
Stacey JS, Kramers JD (1975) Approximation of terrestrial
lead isotope evolution by a two-stage model. Earth Planet
Sci Lett 26: 207–221
Streckeisen A (1974) Classification and nomenclature ofplutonic rocks. Geol Rundsch 63: 773–786
Sun SS, McDonough WF (1989) Chemical and isotopic
systematics of oceanic basalts: implications for mantle
composition and processes. In: Saunders AD, Norry M(eds) Magmatism in Ocean Basins. Geological Societyof London Special Publications 42: 313–345
Sylvester PJ (1998) Post-collisional strongly peraluminous
granites. Lithos 45: 29–44
Tatsumi Y, Eggins S (1995) Subduction Zone Magmatism.
Frontiers in Earth Sciences, Blackwell, Cambridge,
Mass., pp 1–211
Tiepolo M, Oberti R, Vannucci R (2002) Trace-element
incorporation in titanite: constraints from experimentally
determined solid/liquid partition coefficients. Chem Geol
191: 105–119
Tiepolo M, Oberti R, Zanetti A, Vannucci R, Foley S
F (2007) Trace-element partitioning between amphibole and silicate melt. In: Hawthorne F C, Oberti
R, Della Ventura G, Mottana A (eds) Amphiboles.
Crystal chemistry, Occurrence and Health Issues.
Mineralogical Society of America and Geochemical
Society Reviews in Mineralogy and Geochemistry
67: pp 417–452
Tournon J (1984) Magmatismes du Mesozoique a l’actuelen Amerique Centrale: l’example de Costa Rica, desophiolites aux andesites. Unpublished PhD. Thesis,
Université Pierre et Marie Curie, France, pp 1–335
Ulloa A, Delgado C (2010) Características geoquímicas ymineralogía del flanco Pacífico central de la Cordillera
de Talamanca: implicaciones para la evolución de una
corteza continental. Unpublished Thesis, Universidad de
Costa Rica, San José, pp 1–135
Villegas FA (1997) Geodinamica de la Cordillera de
Tilarán, relacion entre la volcanologia y la tectonica.

Unpublished manuscript, Universidad de Costa Rica,
San José, pp 1–147
Villegas FA (2004) La formación Alto Palomo: flujos
pumíticos de la Cordillera Volcánica Central, Costa Rica.
Rev geol Amer Central 30: 73–81
Vogel TA, Patino LC, Alvarado GE, Gans PB (2004) Silicic ignimbrites within the Costa Rican volcanic front:
evidence for the formation of continental crust. Earth andPlanetary Science Letters 226: 149–159
Vogel TA, Patino LC, Eaton JK, Valley JW, Rose WI,
Alvarado GE, Viray E L (2006) Origin of silicic magmas along the Central American volcanic front: genetic
relationship to mafic melts. J Volcanol geotherm Res
156: 217–228
Vogel TA, Patino LC, Alvarado GE, Rose WI (2007) Petrogenesis of ignimbrites. In: Bundschuh J, Alvarado GE(eds) Central America: Geology, Resources, and Hazards.
Taylor & Francis, London, pp 591–618
Wasserburg GJ, Jacobsen SB, DePaolo DJ, McCulloch
MT, Wen T (1981) Precise determination of Sm/Nd ratios,
Sm and Nd isotopic abundances in standard solutions.
Geochim Cosmochim Acta 45: 2311–2324
Watson EB, Harrison TM (1983) Zircon saturation revisited: temperature and composition effects in a variety ofcrustal magma types. Earth Planet Sci Lett 64: 295–304
Weyl R (1980) Geology of Central America. Gebrüder
Bornträger, Berlin, pp 1–371
Wolf MB, Wyllie PJ (1994) Dehydratation-melting ofamphibolite at 10 kbar: the effects of temperature andtime. Contrib Mineral Petrol 115: 369–383
Wones DR (1989) Significance of the assemblage titanite+ magnetite + quartz in granitic rocks. Amer Miner 74:
744–749
Žáček V, Kycl P, Huapaya S, Pécskay Z, Vorel T, Mixa
P, Grygar R, Metelka V, Hradecký, P, Ševcík J (2008)
Resultados preliminares del levantamiento geológico dela hoja Miramar, escala 1 : 50 000. Cooperación geológica
Costa Rica–República Checa. Memoria: Programa yresúmenes, IX Congreso Geológico de América Central
y VI Congreso geológico Nacional, 02–04 Julio, 2008,
San José, Costa Rica, p 212
Žáček V, Vorel T, Kycl P, Huapaya S (2010a) Mapa geológico 1 : 50 000, hoja 3246-II Miramar, República deCosta Rica. Czech Geological Survey, Prague, ISBN
978-80-7075-743-7
Žáček V, Čech S, Havlíček P, Vorel T, Dudík Schulmannová B, Kycl P, Huapaya S (2010b) Mapa geológico
1 : 50 000, hoja 3246-III Chapernal, República de Costa
Rica. Czech Geological Survey, Prague, ISBN 978-807075-744-4
Žáček V, Čech S, Dudík Schulmannová B, Vorel T, Kycl
P, Huapaya S (2010c) Mapa geológico 1 : 50 000, hoja
3246-IV Juntas, República de Costa Rica. Czech Geological Survey, Prague, ISBN 978-80-7075-745-1
79